Question

If f(x) varies directly with x, and f(x) = 56 when x = 8, find the value of f(x) when x = 2

A.
4

B.
7

C.
8

D.
14

Answer 1

f(x) varies directly with x, i.e.

f(x) a x --- Introducing an equal sign: "=" brings in a constant, k, i.e.

f(x) = kx,

f(x)/x = k

When x = 8 & f(x) = 56, then

k = 56/8

k = 7

=> To find f(x), when x = 2 takes you back to the equation: f(x) = kx, where k = 7 & x

= 2, then by substitution you'll have
f(x) = 7 * 2

y = 14 (d).