136hosakote Maths
136hosakote Maths
1.Write cot-1(
1
) in simplest form. 2. Prove that 2Sin-1 x = Sin-1 (2x √ 1−x 2 )
√ x −1
2
Put x = sin θ or θ = sin x -1
√
2
2 x = π -θ = π - sec -1 x
2 sin
√ 1−cos x 2 2 2
Tan-1 ( )= tan-1 ( )
1+cos x
2 cos
2 x
9. Prove that 2 sin-1 3 = tan -1 24
2 5 7
x x 3 3 3
= tan -1 ( tan )= Let sin-1 = θ => sin θ = => tan θ =
2 2 5 5 4
10. Find the value of tan ( √ 3 ) - sec (-2)
-1 -1
2 tan θ 2.3 / 4 24
we know tan 2θ = = =
Let tan -1 ( √ 3 ) = π and sec-1 (-2) = π - π 1−tan2 θ 1−9/16 7
3 3
tan -1 ( √ 3 ) - sec-1 (-2)= π - (π - π ) 24 3 24
3 3 2θ = tan -1 or 2 sin-1 = tan -1
− π 7 5 7
=
3
1. Find the area of the triangle whose vertices are 2. Find the area of the triangle whose vertices are
(3, 8) , (-4, 2) and (5, 1). (1, 0) , (6, 0) and (4, 3).
| | | | | | | |
x1 y1 1 3 8 1 x1 y1 1 1 0 1
1 1 1 1
Let ∆= x2 y2 1 = −4 2 1 Let ∆= x2 y2 1 = 6 0 1
2 2 2 2
x3 y3 1 5 1 1 x3 y3 1 4 3 1
1 1 15
= [ 3(2-1)- 8(-4-5) + 1(-4-10)] ∆ = [ 1(0-3)- 0 + 1(18-0)] = sq units
2 2 2
1 61 4. Find the area of the triangle whose vertices are
∆= [3+72-14 ] = sq units
2 2 (2, 7) , (1, 1) and (10, 8).
| | | |
3.Find the area of the triangle whose vertices are x1 y1 1 2 7 1
1 1
(-2, -3) , (3, 2) and (-1, -8). Let ∆= x2 y2 1 = 1 1 1
2 2
x3 y3 1 10 8 1
| | | |
x1 y1 1 −2 −3 1
1 1 1 47
Let ∆= x2 y2 1 = 3 2 1 ∆ = [ 2(1-8)- 7(1-10) + 1(8-10)] =
2 2 2 2
x3 y3 1 −1 −8 1
5. Find the equation of the line joining the (1, 2) and
1 (3, 6) using determinants.
| |
= [ -2(2+8)+3(3+1) + 1(-24+2)] 1 2 1
2
Let ∆ = 0 => 3 6 1 = 0
1 30 x y 1
∆= [-20+12-22 ] = =15 sq units
2 2 1( 6 – y ) -2 ( 3 – x ) + 1 ( 3y – 6x) = 0
6 -6y -6 + 2x + 3y – 6x =0
6. Find the equation of the line joining the (1, 3) -4x -3y = 0 or 4x + 3y = 0
and (0, 0) using determinants.
7. If the area of the triangle whose vertices are
| |
1 3 1 (-2 ,0) ,( 0,4) and (0, k) is 4 sq. units. Find value of k.
Let ∆ = 0 => 0 0 1 =0
| |
−2 0 1
x y 1 Given ∆ = ± 4 => 0 4 1 =±8
0 k 1
1( 0 – y ) -3 ( 0 – x ) + 1 ( 0 – 0) = 0
- y + 3x =0 OR y = 3x -2(4 – k ) - 0 + 1(0 – 0 ) = ± 8 => -8 + 2k = ± 8
8. Find the equation of the line joining the (3, 1) k=8 k=0
and (9, 3) using determinants. 9. Find the value of k if the area of the triangle is 4 sq.
units and vertices are ( k, 0) , (4, 0) and (0,2).
| |
3 1 1
| |
Let ∆ = 0 => 9 3 1 =0 k 0 1
1
x y 1 Given ∆ = ± 4 => 4 0 1 =±4
2
0 2 1
3( 3– y ) -1( 9 – x ) + 1 ( 9y– 3x) = 0 k(0 – 2) - 0 + 1(8 – 0 ) = ± 8
9 -3y – 9 + x + 9y - 3x =0 -2k + 8 = ± 8
-2x +6y = 0 or x – 3y = 0
=> -2k +8= 8 or - 2k+8 = -8
=> k = 0 OR k=8
1. A relation R on the set A = {1, 2, 3......14} is defined 2. A relation R in the set N of natural number defined
as R = {(x, y) : 3x – y =0}. Determine whether R is as R = {(x, y) : y = x + 5 and x <4}. Determine whether
reflexive, symmetric and transitive. R is reflexive, symmetric and transitive.
R = {( 1 , 3 ) , ( 2 , 6 ) ,( 3 , 9 ),( 4 ,12 )} R = {( 1 , 6 ), ( 2, 7 ) , ( 3 , 8 )}
since (1 ,1)∉R R is not reflexive since (1 ,1)∉R , R is not reflexive
Let (1 ,3)∈R but (3 , 1)∉R Let (1 ,1)∈R but (6 , 1)∉ R
There fore R is not symmetric There fore R is not symmetric
Let (1 ,3)∈R and (3 , 9)∈R but (1 , 9)∉ R By definition of transitivity
There fore R is not transitive R is transitive
3. Determine whether R, in the set A of human beings 4. Relation R in the set Z of all integers is defined as
in a town at a particular time is given by R = {(x, y) : x – y is an integer}. Determine whether R
R = {(x, y) : x and y work at the same place} is reflexive, symmetric and transitive .
since x and x work at the same place Since x – x = 0 is an integer
..˙ ( x , x)∈ R Hence R is reflexive ..˙ ( x , x)∈ R Hence R is reflexive
Let ( x , y )∈ R => x and y work at same place Let ( x , x)∈ R => x – y is an integer
=> y and x also work at the same place ꞊> y – x is also an integer
=> ( y , x )∈R R is symmetric ꞊> ( y , x )∈ R , R is symmetric
Let ( x , y )∈ R and ( y , z )∈R Let Let (x , y )∈R and ( y , z )∈R
=>x and y work at the same place and
=> x – y is an integer and y – z is an integer
y and z work at the same place
=> x and z work at the same place => x- z is an integer
..˙ (x , z)∈R , R is transitive ..˙ ( x , z)∈R R is transitive
Hence R is an equivalence relation Hence R is an equivalence relation
5. A relation ‘R’ is defined on the set A = {1, 2, 3, 4, 5} 6. Show that the relation R in R, the set of reals
as R = {(x, y) : y is divisible by x}. Determine whether defined as R = {(a, b) : a ≤ b} is reflexive and
R is reflexive, symmetric, transitive . transitive but not symmetric.
Since x is divisible by x itself since a ≤ a is true
..˙ ( x , x)∈ R Hence R is reflexive ..˙ (a , a)∈R Hence R is reflexive
Let (1 ,3)∈R but (3 , 1)∉R Let (a , b)∈R => a≤b
Therefore R is not symmetric => but b ≤ a is not true
Let ( x , y )∈ R and ( y , z )∈R (b , a)∉R , R is not symmetric
꞊> y is divisible by x and z is divisible by y Let (a , b)∈R and (b , c)∈R
꞊>z is divisible by x ꞊> (x , z)∈R
=> a ≤ b and b ≤ c => a≤c
Therefore R is not transitive ..˙ (a , c)∈R R is transitive
[31 −15 ] = [33 −13 ] + [−20 20] [−11 52] = [12 22] + [−30 30 ]
↑ symmetric ↑ skew-symmetric
↑ symmetric ↑ skew-symmetric
19.Find
dy
dx
if x = 4t , y =
4
t xy = √a(sin
−1
x)
√a
−1
(cos x)
= √ a
(π )
2
4 differentiate w . r. t. x
x = 4t , y=
t
dy dy −y
dx dy −4 dy −1 x + y . 1= 0 OR =
=4 , = dx dx x
dt dt t
2
dx t
2
| |
^i ^i k^
Let ⃗ a X ⃗ b = 1 −1 3 = 20 ^i +5 ^j -5 k^ => |⃗a X ⃗b| = √ 400+25+25
2 −7 1
The area of a parallelogram = |⃗a X ⃗
b| = √ 450 or 15 √ 2 sq .units.
4. If ⃗a = 5 ^i - ^j -3 k^ and ⃗b = ^i +3 ^j -5 k^ , then show that the vectors a + ⃗
⃗ b
and a - ⃗
⃗ b are perpendicular .
Let ⃗ ⃗
a + b =6 i ^ ^j - 8 k^ and ⃗
+2 b = 4 ^i -4 ^j +2 k^
a - ⃗
Now ( ⃗ a + ⃗ b ).( ⃗a ⃗ -
b )= 24 -8 -16 = 0
Hence , the vectors ⃗a ⃗
b and a⃗ - ⃗
+ b are perpendicular .
5. Find the angle between two vectors ⃗a and b⃗ with magnitudes 1 and 2 respectively
and when ⃗a . ⃗b=1 .
Given |⃗a| = 1 , |⃗b| = 2 and ⃗a . ⃗b =1
a . b⃗
⃗ 1 1 π
W.K.T cos θ = => cos θ = => θ = cos-1 ( )=
|⃗a||⃗b| 1.2 2 3
6. If for a unit vector ⃗a , ( ⃗x - ⃗a ) . ( ⃗x + ⃗a ) = 12 then find |⃗x| .
Given ( ⃗x - ⃗ a ) = 12 and |⃗a| = 1
a ) . ( ⃗x + ⃗
2 2
|⃗x| - |⃗a| = 12 => |⃗x|2 = 13 => |⃗x| = √ 13
7.Find the area of a parallelogram whose adjacent sides are given by 3 ^i + ^j + 4 k^
and ^i - ^j + k^ .
| |
^i ^i k^
Let ⃗ a X b = 3 1 4 = 5 ^i + ^j - 4 k^
⃗ => |⃗a X ⃗b| = √ 25+1+16
1 −1 1
The area of a parallelogram = |⃗a X ⃗
b| = √ 42 sq .units.
8. Show that the vectors 2 ^i -3 ^j +4 k^ and -4 ^i +6 ^j -8 k^ are collinear .
Given a = 2 ^i -3 ^j +4 k^
⃗ and b = -4 ^i +6
⃗ ^j -8 k^
since ⃗ ^ ^
b = -2( 2 i -3 j +4 k )^ => ⃗b = -2 ⃗
a
Hence , the given vectors are collinear .
| |
i^ i^ k^
Let a X ⃗
⃗ b = 1 −7 7 = 0 ^i +19 ^j +19 k^ => |⃗a X ⃗
b| = √ 0+(19)2 +(19)2
3 −2 2
|⃗a X ⃗b| = 19 √ 2
b are such that |⃗a|=2 , |⃗b|=3 and ⃗
a and ⃗
11. If two vectors ⃗ b = 4 then find |⃗a−⃗b| .
a . ⃗
2 2
W.K.T |⃗a −⃗b| = |⃗a|2 + |⃗b| - 2 a⃗ . ⃗b
2
|⃗a −⃗b| = 4 + 9 - 2.4 = 5 => |⃗a−⃗b| = √ 5
12. Find the angle between two vectors ⃗ a and ⃗ b with magnitudes √ 3 and 2 respectively
and when ⃗a . ⃗b=√ 6 .
Given |⃗a| = √ 3 , |⃗b| = 2 and ⃗a . ⃗b = √ 6
a .⃗
=> cos θ = √ √3 √2
⃗ b 6 1
W.K.T cos θ = = => θ = cos-1 ( )= π
⃗
|⃗a||b| √ 3 .2 √3 . √2 . √2 √2 4
13. If ( 2 ^i +6 ^j +27 k^ ) X ( ^i +λ ^j +μ k^ ) = 0 , then find the value of λ and µ .
Given cross product of two vectors is 0. This is possible iff one vector is multiple of other.
Hence 2λ = 6 and 2µ = 27 => λ = 3 and µ = 27/ 2
14. The projection of the vector ⃗ a = 2 ^i +3 ^j +2 k^ on the vector ⃗ b = ^i +2 ^j + k^ .
Let ⃗ a =2 ^i +3 ^j +2 k^ b⃗ = ^i +2 ^j + k^
a . ⃗
⃗ b = 2+6+2 = 10 and |⃗b| = √ 1+4 +1 = √ 6
a .⃗
⃗ b 10
Projection of ⃗ a on ⃗ b = =
⃗
|b| √6
15. Find ⃗ a and ⃗ b , if a +⃗
(⃗ a −⃗
b) .(⃗ b)=8 and |⃗a|=8|⃗ b| .
2
a +⃗ a −⃗ b)=8 and |⃗a|=8|⃗ b| => |⃗a| =64|⃗ b|
2
Given (⃗ b).(⃗
2 2 2 2
|⃗a|2 - |⃗b| = 8 => 64|⃗
b| - |⃗b| = 8 => 63 |⃗b| = 8
=> |⃗b| =
√ 8
63
and
√
|⃗a| = 8
8
63
16. Show that the points A( -2 ^i +3 ^j +5 k^ ) , B ( ^i +2 ^j +3 k^ ) and
C( 7 ^i - k^ ) are collinear .
Let AB⃗ = OB ⃗ - OA ⃗ =3 ^i - ^j - 2 k^ , BC ⃗ = 6 ^i -2 ^j - 4 k^ , AC
⃗ = 9 ^i -3 ^j - 6 k^
⃗
|AB| = √ 14 , ⃗
|BC| = √ 56 = 2 √ 14 ⃗
, |AC| = √ 126 = 3 √ 14
⃗ ⃗
Clearly |AB| + |BC| = |AC| ⃗
Hence , the given points are collinear.
x +2 y −4 z−5
= = be the cartesian form of the line .
3 5 6
3. Find the angle between the pair of lines given by
⃗r = 3 ^i +2 ^j - 4 k^ +λ( ^i +2 ^j +2 k^ ) and ⃗r =5 ^i - 2 ^j + μ (3 ^i +2 ^j +6 k^ )
Given b⃗1 = ^i +2 ^j +2 k^ and b⃗2 = 3 ^i +2 ^j +6 k^
|b⃗1| = √ 9 =3 , |b⃗2| = √ 9+ 4+36 =7 , b⃗1 . b⃗2 = 3+4+12 =19
b⃗1 . b⃗2 19 19
W.K.T cos θ = => cos θ = => θ = cos-1 ( )
|b 1||b2|
⃗ ⃗ 3.7 21
4. Find the angle between the pair of lines given by
⃗r = 2 ^i -5 ^j + k^ + λ ( 3 ^i +2 ^j +6 k^ ) and ⃗r = 7 ^i - 6 k^ + μ ( ^i +2 ^j +2 k^ )
Given b⃗1 = 3 ^i +2 ^j +6 k^ and b⃗2 = ^i +2 ^j +2 k^
|b⃗1| = √ 9+ 4+36 =7 , |b⃗2| =3 , b⃗1 . b⃗2 = 3+4+12 =19
b⃗1 . b⃗2 19 19
W.K.T cos θ = => cos θ = => θ = cos-1 ( )
|b⃗1||b⃗2| 7.3 21
5. Find the angle between the pair of lines given by ⃗r = 3 ^i + ^j - 2 k^ + λ ( ^i - ^j - 2 k^ )
and ⃗r =2 ^i - ^j - 56 k^ + μ ( 3 ^i -5 ^j - 4 k^ )
Given b⃗1 = ^i - ^j -2 k^ and b⃗2 = 3 ^i -5 ^j -4 k^
|b⃗1| = √ 6 , |b⃗2| = √ 9+25+16 = 5 √ 2 , b⃗1 . b⃗2 = 3+5+8= 16
b⃗1 . b⃗2 16 8
W.K.T cos θ = => cos θ = => θ = cos-1 ( )
|b⃗1||b⃗2| √6 5 √2 5 √3
x +3 y −1 z +3 x +1 y −4 z−5
6. Find the angle between the pair of lines = = and = = .
3 5 4 1 1 2
⃗ ^ ^ ^ ⃗
Given b1 =3 i +5 j +4 k and b2 = i + j +2 k ^ ^ ^
|b⃗1| = 5 √ 2 , |b⃗2| = √ 6 , b⃗1 . b⃗2 = 3+5+8= 16
b⃗1 . b⃗2 16 8
W.K.T cos θ = => cos θ = => θ = cos-1 ( )
|b 1||b2|
⃗ ⃗ 5 √2 √6 5 √3
7. Find the angle between the pair of lines whose direction ratios are a , b , c and b –c , c –a , a –b .
Since the dot product of given vectors = a.(b – c) + b.(c –a) + c.(a – b) = a.b –a.c + b.c – c.b + c.a – c.b = 0
cos θ = 0 or lines are perpendicular and hence θ = π
2
A-1 = 4 I – A
A-1 =
4 0
0 4
– [ ] [ ]
2 3
1 2
=> A-1 =
2 −3
−1 2 [ ]
2. Show that the matrix A =
3 2
1 1 [ ]
satisfies the equation A2 – 4 A + I = O . where I is the 2 X 2
identity matrix and O is the 2 X 2 zero matrix . Using this equation , find A -1 .
Given A = [ ]
3 2
1 1
=> A2 =
3 2
1 1 [ ] [ ] [
3 2
1 1
=
9+2 6 +2
3+1 2+1
=
11 8
4 3 ] [ ]
Let A2 – 4 A + I = [114 83] – [124 84 ] + [10 01] = [00 00] = O
Hence , A2 – 4 A + I = O
Now I= 4A – A2
ly -1
X A , A I = 4 A-1 A - A-1 A.A
-1
A-1 = 4 I – A
A-1 =
4 0
0 4
– [ ] [ ]
3 2
1 1
=> A-1 =
1 −2
−1 3 [ ]
3. Show that the matrix A =
3 1
−1 2 [ ]
satisfies the equation A2 – 5 A + 7 I = O . where I is the
2 X 2 identity matrix and O is the 2 X 2 zero matrix . Using this equation , find A -1 .
Given A = [ 3 1
−1 2 ]
=> A2 =
3 1
−1 2 [ 3 1
−1 2 ] [ =
9−1
] [
−3−2 −1+4
3+2
=
8 5
−5 3 ] [ ]
Let A2 – 5 A + 7I = [−58 53] – [−515 105 ] + [70 70] = [00 00] = O
Hence , A2 – 5 A + 7I = O
Now 7I = 5A – A2
ly -1
X A , 7 A-1 I = 5 A-1 A - A-1 A.A
7 A-1 = 5 I – A
7 A-1 =
5 0
0 5
–[ ] 3 1
−1 2 [ ] => 7 A-1 = [21 −13 ]
[ ]
2 −1
A-1 =
1
7 [
2 −1
1 3
OR ] A-1 = 7
1
7
3
7 7
⃗r −⃗a m
= => n( ⃗r −⃗a ) = m( ⃗
b−⃗r )
⃗
b−⃗r n
m⃗ b +n ⃗a
=> ( m + n ) ⃗r = m ⃗
b +n ⃗
a => ⃗r =
m+n
2. Show that the vector ^i + ^j + k^ is equally inclined to the axes OX , OY and OZ.
Ans : Given ^i + ^j + k^ then direction ratios are 1 , 1 , 1 and
1 1 1
direction cosines are , ,
√3 √3 √3
1 1 1
i.e, cos ɑ = , cos β = , cos γ =
√3 √3 √3
1
=> ɑ = β = γ = cos -1
√3
^ ^ ^
Hence , the vector i + j + k is equally inclined to the axes OX , OY and OZ.
3. If ⃗ a , ⃗b , ⃗c are three unit vectors such that ⃗ a +⃗ b +⃗c =0 . Find the value of ⃗ a .⃗
b +⃗
b . ⃗c +⃗
c .⃗
a .
Ans : Given ⃗ a +⃗ b +⃗c =0 and |⃗a|=|⃗ b|=|⃗ c|=1
2
(⃗a + ⃗b+⃗c )2=0 => |⃗a| +|⃗ b| +|⃗c| +2 ( ⃗ a .⃗
b +⃗
2 2
b . ⃗c +⃗c .⃗
a )=0
−3
a .⃗
⃗ b +⃗ b . ⃗c +⃗c .⃗
a =
2
4. If ⃗ ⃗
a , b ,⃗c satisfy the condition ⃗ a +⃗b +⃗c =0 and |⃗a|=1 , |⃗b|=4 and |⃗c|=2 ,
Evaluate µ = ⃗ a .⃗
b +⃗ b .⃗c +⃗ c .⃗a .
Ans : Given ⃗ a +⃗ b +⃗c =0 and |⃗a|=1 , |⃗b|=4 and |⃗c|=2
2
(⃗a + ⃗b+⃗c ) =0 => |⃗a| +|⃗ b| +|⃗c| +2 ( ⃗ a .⃗b +⃗
2 2 2
b . ⃗c +⃗
c .⃗a )=0
1 + 16 + 4 + 2 ( ⃗ ⃗ ⃗
a . b + b . ⃗c +⃗c .⃗
a )=0
−21
Therefore , µ= ⃗ a .⃗b +⃗
b .⃗c +⃗ c .⃗a =
2
5. Let ⃗ ⃗ |⃗ |
a , b , ⃗c are three vectors such that |⃗a|=3 , , b =4 and |⃗c|=5 and each of them being
perpendicular to the sum of others two , find |⃗a + ⃗ b +⃗c|
Ans : Given ⃗ a ┴ ( ⃗ b +⃗ c ), ⃗ b ┴ ( ⃗c +⃗ a ) , ⃗c ┴ ( ⃗ a +⃗ b )
=> a . ( b +⃗
⃗ ⃗ ⃗
c ) = 0 , b . ( ⃗c +⃗ a ) = 0 , ⃗c . ( ⃗ ⃗
a +b ) = 0
adding these 2 ( ⃗ ⃗ ⃗
a . b + b . ⃗c +⃗ c .⃗a )=0
2 2 ⃗2
⃗
Now , |⃗a + b +⃗c| = |⃗a| +|b| +|⃗c| +2 ( ⃗ a .⃗
b +⃗
2
b . ⃗c +⃗c .⃗ a )
2
|⃗a + ⃗b +⃗c| =9 + 16 + 25 + 0 = 50 => |⃗a + ⃗ b+⃗c| = √ 50 or 5 √2
6. If ⃗ a = 2 ^i +2 ^j +3 k^ , ⃗ b = - ^i +2 ^j + k^ and ⃗c = 3 ^i + ^j are such that
a +λ ⃗
⃗ b is perpendicular to ⃗c , then find the value of λ .
Ans : Given ⃗ a +λ ⃗ b is perpendicular to ⃗c => ( ⃗ a +λ ⃗ b ) . ⃗c = 0
=> ^ ^
[ 2 i +2 j +3 k + λ (- i +2 j + k )] . ( 3 i + ^j ) = 0
^ ^ ^ ^ ^
=> ( 2 – λ ) 3 + (2 + 2λ ) 1+ ( 3 + λ ) 0 = 0
=> 6–3λ+ 2+2λ+0=0
=> – λ+8=0 => λ = 8
| |
^i ^i ^k
⃗c X ⃗ d = 2 3 4 = -2 ^i +4 ^j -2 k^ = 2( - ^i +2 ^j + k^ )
0 −1 −2
⃗
|⃗c X d| = 2 √ 1+4+1 = 2 √ 6
⃗c X ⃗
d 2
unit vector perpendicular to each of the vectors ⃗c and ⃗ d is = ( - ^i +2 ^j + k^ )
⃗
|⃗c X d| 2 √6
1
Therefore , required vector is ( - ^i +2 ^j + k^ )
√6
8. Find a unit vector perpendicular to each of the vectors a⃗ + ⃗ b and ⃗ a −⃗b , where
a =5 ^i− ^j−3 k^ and ⃗
⃗ b= ^i +3 ^j−5 k^ .
Ans : Let ⃗c = ⃗ a +⃗ b = 6 ^i +2 ^j−8 k^ and ⃗ = ⃗
d a −⃗b = 4 ^i −4 ^j+2 k^
| |
^i ^i ^k
⃗c X ⃗ d = 6 2 −8 = -28 ^i - 44 ^j -32 k^ = 4( -7 ^i -11 ^j -8 k^ )
4 −4 2
⃗
|⃗c X d| = 4 √ 49+121+64 = 4 √ 234
⃗c X ⃗
d 4
unit vector perpendicular to each of the vectors ⃗c and ⃗ d is = (-7 ^i -11 ^j -8 k^ )
⃗
|⃗c X d| 4 √ 234
1
Therefore , required vector is ( -7 ^i -11 ^j -8 k^ )
√ 234
9. Find the area of the triangle whose vertices A( 1 , 1 , 2 ) , B( 2 , 3 , 5 ) and C( 1 , 5 , 5 )
by using vector method.
Ans : Let AB ⃗ = OB ⃗ - OA ⃗ = (2 – 1 ) ^i +( 3 – 1 ) ^j +( 5 – 2 ) k^ = ^i + 2 ^j +3 k^
⃗ = OC
AC ⃗ = (1 – 1 ) ^i +( 5 – 1 ) ^j +( 5 – 2 ) k^ = 0 ^i + 4 ^j + 3 k^
⃗ - OA
| |
^i ^i k^
Now , ⃗ X
AB ⃗ =
AC 1 2 3 = - 6 ^i - 3 ^j + 4 k^
0 4 3
⃗ X AC
|AB ⃗ | = √ 36+9 +16 = √ 61
Area of triangle =
1 ⃗ | = √ 61
⃗ X AC
|AB
2 2
10. Find a unit vector perpendicular to each of the vectors ⃗ a +⃗
b and ⃗ a −⃗b , where
a =3 ^i +2 ^j+2 k^ and ⃗
⃗ b= ^i +2 ^j−2 k^
Ans : Let ⃗c = ⃗ a +⃗b = 4 ^i +4 ^j+0 k^ and ⃗ a −⃗b = 2 ^i +0 ^j+ 4 k^
d = ⃗
| |
^i ^i k^
⃗
⃗c X d = 4 4 0 = 16 ^i - 16 ^j -8 k^ = 8( 2 ^i -2 ^j - k^ )
2 0 4
⃗
|⃗c X d| = 8 √ 4+ 4+1 = 24
⃗c X ⃗d 8
unit vector perpendicular to each of the vectors ⃗c and ⃗ d is = ( 2 ^i -2 ^j - k^ )
|⃗c X ⃗d| 24
1
Therefore , required vector is ( 2 ^i -2 ^j - k^ )
3
= A e mx [ m2 - ( m + n )m + mn ] + B e nx [ n2 - ( m + n )n + mn ]
= A e mx [ m2 - m2 - mn + mn ] + B e nx [ n2 - mn - n2 + mn ]
d2 y dy
Hence , 2
−(m+n) +m n y=0
dx dx
2
d y dy 1
=> √ 1− x 2 + (-2x) =0
dx 2 √ 1− x
2 2
dx
2
2 d y dy
=> Multiply by √ 1− x 2 , (1−x ) − x =0
dx 2
dx
2 2
6. If ey ( x + 1 ) = 1 then show that d y2=( dy ) .
dx dx
y
Ans : Given e ( x + 1 ) = 1 -------(1)
dy dy
Differentiate , e y( 1 ) + ( x + 1 ) e y = 0 => e y + 1. =0 using (1)
dx dx
dy
=-ey -----------(2)
dx
2
d y dy dy dy
Differentiate , =-ey = . using (2)
dx
2
dx dx dx
d2 y dy 2
=> =( ) Hence, the result .
dx
2
dx
2
−1
d y dy
7. If y = e acos x , ( -1 ≤ x ≤ 1 ) then show that (1−x 2 ) − x −a2 y=0 .
dx 2
dx
acos x
−1
dy −1
acos x −a
Ans : Given y = e ----(1) => = e .
dx √ 1− x 2
=> √ 1− x 2 dy dx
= -ay using (1)
2
=> Differentiate , √ 1− x 2 d y2 + dy 1
( - 2 x ) = -a
dy
dx dx 2 √ 1−x 2 dx
2
d y dy dy
=> Multiply by √ 1− x 2 , (1−x 2 ) −x = - a √ 1− x 2
dx
2
dx dx
2
2 d y dy
=> (1−x ) −x = - a ( -a y )
dx 2
dx
2
2 d y dy 2
=> (1−x ) − x −a y=0
dx
2
dx
2
8. If y = ( sin-1 x )2 then show that (1−x 2 ) d y2− x dy =2
dx dx
−1
dy 2 sin x dy
Given y = ( sin -1 x )2 => = => √ 1− x
2
= 2 sin- 1 x
dx √ 1− x 2 dx
dy 2
=> squaring on both sides (1 – x2 ) ( ) = 4 ( sin -1 x )2 = 4y
dx
2
dy d y dy 2 dy
=> Differentiate , (1 – x2 ) 2 +( ) (-2 x ) = 4
dx dx 2
dx dx
2
dy 2 d y dy
=> Dividing by 2 , we get (1−x ) − x =2
dx dx
2
dx
=4 ∫ y dx =4 ∫ √ a 2− x2 dx
x =a 0
x a2 x
=4{
2
√ a −x
2 2
+
2
sin -1
a
}0a
2 2
a a π
=4{0+ sin -1 1 – (0 +0) } = 4
2 2 2
A = π a2
x2 y2
2. Find the area enclosed by the ellipse 2
+ 2 =1 by using integration .
a b
2 2
x y b
Ans : Given 2
+ 2
=1 => y =
a
√ a 2−x 2
a b
Required Area = 4 ( Shaded Area )
x =b a
b
= 4 ∫ y dx = 4 ∫ √ a2 −x 2 dx
x =a 0 a
b x a2 x
=4
a
{
2
√ 2
a −x +
2
2
sin -1
a
}0a
2
b a
=4 {0+ sin -1 1 – (0 +0) }
a 2
b a2 π
=4
a 2 2
A = π ab
3. Find the area of the region bounded by the line y = 3x + 2 the x – axis and the
ordinates x = -1 and x = 1 .
Ans : Given line is y = 3x + 2 cuts the x-axis at x = -2/3 in (-1 , 1 )
|∫ |
−2/3 1
|( 32x +2 x )|
2 2
3x
= +2 x) -2/31
-1
-2/3 +
(
2
2 4 3 3 2 4
= | - - +2 | + [ +2 - + ]
3 3 2 2 3 3
1 25 13
A = + = sq units
6 6 3
4. Find the area of the region bounded by the curve y2 = 4x , y – axis and the line y = 3 .
Ans : y2 = 4x , y -axis and the line y = 3
Required Area = shaded Area
3 3 2
y
= ∫ x dy = ∫ dy
0 0 4
1 27 9
= [ -0]=
4 3 4
Note : If area of circle in first quadrant means only shaded area ( remove 4 in Q1) and in
ellipse particular values for a and b are given then simply substitute the values in Q 2 .
x− x1 y − y1 z−z 1
= = be the cartesian form of the line .
a b c
Q. NO . 45 ( DETERMINANTS ) 5 mark
1. Solve by matrix method x + y + z = 6 , y + 3 z = 11 , x – 2y + z = 0 .
[ ] [] []
1 1 1 x 6
Ans : Given A = 0 1 3 , X= y , B= 11
1 −2 1 z 0
| A | = 1(1+6) – 1 ( 0 – 3 ) +1 (0 –1) = 9 ≠ 0
[ ]
+(1+6 ) −(0−3) +(0−1)
co-factor matrix = −(1+2) +(1−1) −(−2−1)
+(3−1) −(3−0) +(1−0)
[ ]
7 −3 2
adj A = 3 0 −3
−1 3 1
[ ] []
7 −3 2 6
1 1
X = A-1 B = adj A . B = 3 0 −3 11
|A| 9
−1 3 1 0
[] [ ] [ ] []
x 42−33+0 9 1
1 1
y = 18+0−0 = 18 = 2 x = 1 , y =2 , z = 3
9 9
z −6+33+0 27 3
[ ]
[] []
1 −1 1 x 4
Ans : Given A = 2 1 −3 , X= y , B= 0
1 1 1 z 2
| A | = 1(1+3) + 1 ( 2 + 3 ) +1 (2 –1) = 10 ≠ 0
[ ] [ ] [ ]
+(1+3) −(2+3) +(2−1) 4 −5 1 4 2 2
co-factor matrix = −(−1−1) +(1−1) −(1+1) = 2 0 −2 adj A = −5 0 5
+(3−1) −(−3−2) +(1+2) 2 5 3 1 −2 3
[ ] []
4 2 2 4
1 1
X = A-1 B = adj A . B = −5 0 5 0
|A| 10
1 −2 3 2
[] [ ] [ ] []
x 16+0+ 4 20 2
1 1
y = −20+0+10 = −10 = −1 x = 2 , y =-1 , z = 1
10 10
z 4−0 +6 10 1
3. Solve by matrix method 3x -2 y + 3z = 8 , 2x+y - z = 1 , 4x - 3y +2 z = 4 .
[ ] [] []
3 −2 3 x 8
Ans : Given A = 2 1 −1 , X= y , B= 1
4 −3 2 z 4
| A | = 3(2–3) +2 ( 4+4 ) +3 ( –6–4 ) = – 17 ≠ 0
[ ] [ ] [ ]
+(2−3) −(4 +4) +(−6−4) −1 −8 −10 −1 −5 −1
C.M = −(−4+9) +(6−12) −(−9+8) = −5 −6 1 adj A = −8 −6 9
+(2−3) −(−3−6) +(3+ 4) −1 9 7 −10 1 7
[ ] []
−1 −5 −1 8
1
-1 1
X=A B= adj A . B = −8 −6 9 1
|A| −17
−10 1 7 4
[] [ ] [ ] []
x −8−5−4 −17 1
1 1
y = −64−6 +36 = −34 = 2 x = 1 , y =2 , z = 3
−17 −17
z −80+1+28 −51 3
[ ] [] []
2 3 3 x 5
Ans : Given A = 1 −2 1 , X= y , B = −4
3 −1 −2 z 3
| A | = 2(4+1) - 3( -2 -3 ) +3 ( –1+6 ) = 40 ≠ 0
[ ] [ ] [ ]
+( 4+1) −(−2−3) +(−1+6) 5 5 5 5 3 9
C.M = −(−6+3) +(−4−9) −(−2−9) = 3 −13 11 adj A = 5 −13 1
+(3+6) −(2−3) +(−4−3) 9 1 −7 5 11 −7
[ ][]
5 3 9 5
1 1
X = A-1 B = adj A . B = 5 −13 1 −4
|A| 40
5 11 −7 3
[ ] [ ] []
25−12+27 40 1
1 1
X = 25 +52+3 = 80 = 2 x = 1 , y =2 , z = -1
40 40
25−44−21 −40 −1