Question

If y=7, when x=6, how do you find y when x=-21 given that y varies inversely as x?

Answer 1

`y=color(green)(-2)`

Explanation:

If `y` varies inversely as `x` then
`color(white)("XXX")x xx y=c` for some constant `c`

We are told that `(x,y)=(6,7)` is a solution to the required relation;
so
`color(white)("XXX")6 xx 7 =c color(white)("XX")rarrcolor(white)("XX")c=42`

`color(white)("XXXXXXXXXXX")rarrcolor(white)("XX")x xx y =42`

When `x=-21`
`color(white)("XXX")(-21) xx y = 42color(white)("XX")rarrcolor(white)("XX")y=-2`#