Question

If y varies directly with x, how do you find y when x = 5 if y = -6 when x = 2?

Answer 1

`y=-15`

Explanation:

If `y` varies directly with `x` then
`color(white)("XXX")y/x=c` for some constant `c`

If `y=-6` when `x=2` then
`color(white)("XXX")(-6)/2=c rarr c=-3`

That is `y/x=-3`

So when `x=5`
`color(white)("XXX")y/5=-3`

`color(white)("XXX") rarr y=-3xx5`

`color(white)("XXX") rarr y=-15`