Question

Given that y varies directly with x, and x = -16, y = -4, how do you write a direct variation equation that relates x and y?

Answer 1

For a direct variation:
`color(white)("XXX")y=c*x` for some constant `c`

Since for the required direct variation `(x,y)=(-16,-4)` is a solution:
`color(white)("XXX")(-4)=c*(-16)`

`color(white)("XXX")rarr c=1/4`

Therefore the direct variation equation would be:
`color(white)("XXX")y=1/4x`