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

Explanation:

y-kx

-1=k(3)

/ /

3 3

`(-1)/(3)`=k

y=
`((-1)/(3))`
`(9)\\`

y=-3

Answer 2

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 =
`(y)/(x)` =
`(-1)/(3)` = -
`(1)/(3)`

hence y = -
`(1)/(3)` x

when x = 9, then

y = -
`(1)/(3)` × 9 = - 3