Series and Proofs Questions 0525
Series and Proofs Questions 0525
2)
3)
5)
6)
=
9
10)
)
12)
13
14)
15)
16)
18)
(a)
as
2)
2. [Maximum mark: 6]
(a) Find the value of sum
39 + 48 + 57 + 66 + L + 246. [3 marks]
n
(b) This sum can be expressed in the form ∑ (ak + b) .
k =1
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2
3. [Maximum mark: 6]
Consider the infinite geometric series
1 1 3
− 2
+ +L
3k 3 6k 12k 3
(a) Find the possible values of k given that the series converges. [4 marks]
(b) Find the exact value of the infinite sum for k = 1. [2 marks]
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3
4. [Maximum mark: 7]
In an arithmetic sequence the sum of the first six terms is 75 and the sum of
the first ten terms is 185.
(a) Find the sum of the first eight terms. [5 marks]
(b) Find the number of terms which are less than 1000. [2 marks]
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4
5. [Maximum mark: 5]
The third term of an infinite geometric sequence is –108 and the fifth term is –72.
Find the possible values for the sum to infinity of the sequence.
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5
6. [Maximum mark: 7]
The value of a share decreases by 2% each day. Its value today is 680€.
Find
(a) the value of the share after 9 days. [2 marks]
(b) the value of the share 10 days ago. [2 marks]
(c) after how many days the value of the share will fall below 400€ [3 marks]
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6
7. [Maximum mark: 8]
(a) In an arithmetic sequence, the sum of the first ten terms is equal to the tenth
term. Find S 9 and u 5 . [5 marks]
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7
8. [Maximum mark: 6]
The sum of the first n terms of a series is given by
S n = n 3 + n where n ∈ +.
(a) Find the first three terms of the sequence and show that it is
neither arithmetic nor geometric. [4 marks]
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8
9. [Maximum mark: 8]
(a) Consider the expansion of
8
3 3
x −
x
Find
(i) Find the constant term.
(ii) Find the term in x 4 . [5 marks]
x
Find the term in x 4 . [3 marks]
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9
10. [Maximum mark: 6]
In the expansion of
n
3
x 3 1 −
x
the constant term is – 3240. Find
(a) the value of n. [4 marks]
(b) the coefficient of x. [2 marks]
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10
11. [Maximum mark: 8]
The distinct numbers
x + 9y , x + 3y , x
are the first three terms of a geometric sequence.
(a) Find the common ratio. [5 marks]
(b) Given that the sum to infinity is 48, find the values of x and y. [3 marks]
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11
12. [Maximum mark: 12]
1 2 3 n
Let Sn = + + + L +
2! 3! 4! (n + 1)!
(a) Calculate S1 , S 2 , S 3 , S 4 [2 marks]
(b) Write down the values of 1!, 2!, 3!, 4!, 5! [2 marks]
(c) Hence, guess a formula for S n , for any n ∈ Z + [1 mark]
(d) Show by using mathematical induction that your guess is true. [7 marks]
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12
13. [Maximum mark: 15]
(a) Express ( 3+ 2 ) 3
in the form a 2 + b 3 where a, b ∈ Z + [2 marks]
(b) Express ( 2) ( )
2 4
3+ and 3+ 2 in the form a + b 6 ,
+
where a, b ∈ Z [3 marks]
+
(c) By using mathematical induction, show that, for any n ∈ Z
( 3+ 2 )
2n
has the form a + b 6 , where a, b ∈ Z + [7 marks]
(d) Hence show that, for any n ∈ Z +
( 3+ 2 )
2 n +1
has the form a 2 + b 3 , where a, b ∈ Z + [3 marks]
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14
2. [Maximum mark: 5]
Consider the infinite geometric series
r
∞
9 3k + 1
∑
r =1 2 3
(a) Find the possible values of k given that the series converges. [3 marks]
(b) Find the exact value of the infinite sum for k = – 1. [2 marks]
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2
3. [Maximum mark: 6]
In an arithmetic sequence the sixth term is 95 while the sum of the first 21 terms is
3360. Find
(a) the first term which exceeds 1000. [4 marks]
(b) the sum of the terms which are less than 1000. [2 marks]
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3
4. [Maximum mark: 6]
The population of ants in a field today, 10 October 2017, is 120,000 and increases
by 9% each day.
(a) Find the population of ants on 31 October 2017. [3 marks]
This population at some time exceeds 1,000,000.
(b) Write down an inequality to represent this information for the number
of days needed and hence find the date when it will happen. [3 marks]
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4
5. [Maximum mark: 6]
The integers a, b and b+2a are consecutive terms in an arithmetic sequence.
The integers a, 20 and a+5b are consecutive terms in a geometric sequence.
Find the values of a and b.
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5
6. [Maximum mark: 7]
(a) In an arithmetic sequence, the sum of the first ten terms is equal to the sum of
the first 9 terms. Show that
u16 = −u4 [3 marks]
(b) Find the sum of the numbers which are multiples of 8 but not multiples of 6,
between 100 and 3100. [4 marks]
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6
7. [Maximum mark: 6]
The sum of the first n terms of a series is given by
S n = 5n +1 − 5 where n ∈ +.
(a) Find the fifth term of the sequence. [2 marks]
(b) Find the n-th term of the sequence in terms of n. [2 marks]
(c) Show that the sequence is geometric. [2 marks]
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7
8. [Maximum mark: 7]
(a) Find the constant term in the expansion of
10
3 3
x − 2 [3 marks]
x
(b) Find the constant term in the expansion of
10
3 3 1
x − 2 5 + x + 2
3
[4 marks]
x x
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8
9. [Maximum mark: 6]
In the expansion of
(2a + ax ) n
the coefficient of x 4 is five times the coefficient of x 2 . Find the value of n.
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9
10. [Maximum mark: 8]
The numbers a, b and c are the second, the fifth and the eleventh term of an
arithmetic sequence. They are also consecutive terms in an increasing geometric
sequence.
(a) Find the common ratio of the geometric sequence. [5 marks]
(b) Given that the third term of the arithmetic sequence is 20, find the values of
a, b and c . [3 marks]
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10
11. [Maximum mark: 7]
Using mathematical induction, prove that
the number 2 2 n +1 − 6n + 16 is divisible by 18, for any n ∈ Z +
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11
12. [Maximum mark: 10]
(
(a) Express 1+ 2 3 ) 3
in the form a + b 3 where a, b ∈ Z + [2 marks]
(b) By using mathematical induction, show that for any n ∈ Z + ,
(1 + 2 3 ) n
has the form a + b 3
where a is an odd integer and b is an even integer. [8 marks]
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12
2. [Maximum mark: 9]
(a) Prove by mathematical induction that [7]
n
∑r ⋅2
r =2
r
= (n − 1)2 n +1 for any integer n ≥ 2 .
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2
3. [Maximum mark: 7]
Prove by mathematical induction that
(n + 1)!≥ 2 n n for any integer n ≥ 3 .
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Turn over
3
4. [Maximum mark: 8]
A sequence is defined recursively as follows
u1 = 1
u n +1 = 3u n +1
(a) Write down the first four terms of the sequence. [2]
(b) Prove by mathematical induction that
3n − 1
un = for any n = 1,2,3,... . [6]
2
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4
5. [Maximum mark: 10]
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Turn over
5
2. [Maximum mark: 9]
(a) Prove by mathematical induction that [7]
1 ⋅ 21 + 2 ⋅ 2 2 + 3 ⋅ 2 3 + L + n ⋅ 2 n = (n − 1)2 n +1 + 2 for any n ∈ Z + .
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2
3. [Maximum mark: 7]
Prove by mathematical induction that
3 n > n 2 + 2n for any integer n ≥ 2 .
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Turn over
3
4. [Maximum mark: 8]
A sequence is defined recursively as follows
u1 = 5
u n +1 = 2u n +5
(a) Write down the first four terms of the sequence. [2]
(b) Prove by mathematical induction that
un = 5 ⋅ 2n − 5 for any n = 1,2,3,... . [6]
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4
5. [Maximum mark: 10]
(a) Prove by mathematical induction that
n!×[2 × 6 × 10 × 14 × L × (4n − 2)] = (2n)! for any n ∈ Z + . [8]
a!
(b) Express (2 × 6 × 10 × 14 × L × 78) in the form . [2]
b!
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5
2. [Maximum mark: 9]
It is claimed that
1 21 2 2 2 3 2 3 ⋯ n 2 n ( n 1) 2 n 1 2 for any n Z .
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2
3. [Maximum mark: 6]
Prove by mathematical induction that
(2n)! 2n n for any integer n 2 .
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Turn over
3
4. [Maximum mark: 9]
(a) Prove, by using contradiction, that for a, b ℝ {2}
2a 3 2b 3
if a b then [5]
a2 b2
(b) State if the following statement is also true:
2a 2 3 2b 2 3
if a b then 2
a2 2 b 2
Justify your answer, either by giving a proof, or by using a counterexample. [2]
(c) Based on the results in (a) and (b), write down a conclusion for the functions
2x 3 2 x2 3
f ( x) , x 2 and g ( x ) 2 . [2]
x2 x 2
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4
2. [Maximum mark: 6]
Given that
(a − 3 ) 4
= 97 − b 3
where a and b are positive integers, find the value of a and of b. [6 marks]
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Page 2
3. [Maximum mark: 7]
Given that
(2 + x) 5 (1 + 2 x) n = 32 + ax + 27600 x 2 + L + 2 n x n + 5
find the values of the integers a and n. [7 marks]
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Page 3
4. [Maximum mark: 11]
Solve analytically the equations
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Page 4
5. [Maximum mark: 11]
Solve the exponential equations
3 ⋅ (5 x ) ln a
(a) 2 x +5 = x − 2 . Give your answer in the form x = , where a, b ∈ Q . [5 marks]
2 ln b
3
(b) 2 x +5 = 8 + . Give your answer in the form x = a + log 2 b , where a, b ∈ Z . [6 marks]
2 x −2
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Page 5
6. [Maximum mark: 9]
Solve the equations
x ln x x [4+5 marks]
(a) x log x = 10000 (b) 2
=
x e
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Page 6
7. [Maximum mark: 6]
x
It is given that log a ( x 2 y ) = 14 and log a ( )=2
y2
(a) Find log a x and log a y
[5 marks]
(b) Hence find log y x [1 mark]
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Page 7
8. [Maximum mark: 6]
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Page 8
9. [Maximum mark: 11]
Solve the equations
(a) ln x 2 + ln x = 2 [3 marks]
(b) (ln x) 2 + ln x = 2 [4 marks]
(c) (ln x)(ln x)(ln x) = ln x 9 [4 marks]
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Page 9
10. [Maximum mark: 9]
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Page 10
11. [Maximum mark: 12]
(a) Prove by using mathematical induction that
0 1 2 n − 1 n!−1
+ + +L+ = , for any n ≥ 1 . [7 marks]
1! 2! 3! n! n!
6
r −1 1
(b) Given that ∑
r =1 r!
= 1 − find the value of a.
a [2 marks]
n
r −1
(c) Find the smallest value of n so that ∑
r =1 r!
> 0.99999 [2 marks]
n
r −1
(d) Find the largest value of n so that ∑
r =1 r!
< 0.99999 [1 mark]
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Page 11
12. [Maximum mark: 8]
(a) Given the property
ln x + ln y = ln xy
prove by using mathematical induction that
n ln x = ln x n , for any positive integer n. [7 marks]
(b) Is the property true for n = 0 ? [1 mark]
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