Question

How do you find the direct variation equation if y = -16 when x = 4, and how find x when y = 20?

Answer 1

The form of a direct variant equation is
`y=mx` for some constant value `m`

We are given `(x,y) = (4,-16)` is a solution for this equation, so
`-16 = m4`
which tells us
`m=-4`
Our direct variant equation is
`y = (-4)x`

When `y=20`
`20 = (-4)x`
which implies
`x=-5`