2/4/25, 2:36 PM Direct Variation
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Direct Variation
1.1 Direct Variation
Definition of direct variation
Direct variation explains the relationship between two variables, such that when variable y increases, then variable x also increases at the
same rate and vice versa.
This relation can be written as y varies directly as x .
In general, for a direct variation, y varies directly as xn can be written as
x ∝ xn (variation relation) or x = kxn (equation relation)
1 1
where n = 1, 2, 3, , and k is a constant.
2 3
Example 1
Given m = 12 when n = 3.
Express m in terms of n if
a) m varies directly as n.
b) m varies directly as n3 .
Solution:
a) n ⟹ m = kn … (1).
Substitute m = 12 and n = 3 into (1)
12
12 = k(3) ⟹ k = = 4.
3
∴ m = 4n.
b) m ∝ n3 ⟹ m = ln3 … (2).
Substitute m = 12 and n = 3 into (2):
12 4
12 = l(3)3 ⟹ l = =
27 9
4 3
∴m= n .
9
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