Question

If the value of y varies directly with x and y= -1 when x=3, find y if x=9

Answer 1

y = - 3

Since y varies directly as x then

y = kx ← ( k is the constant of variation )

to find k use y = - 1 when x = 3

k = $\frac{y}{x}$ = $\frac{-1}{3}$ = - $\frac{1}{3}$

hence y = - $\frac{1}{3}$ x

when x = 9, then

y = - $\frac{1}{3}$ × 9 = - 3