Since it must include the point (9,-12) we know that if we
substitute x=9 and y=-12 into y = kx we will have a true
equation, so we do that:
y = k·x
-12 = k·9
-12 = 9k
We divide both sides by 9 to solve for k:
=
= k
So the constant k is , and so we substitute that for k in
y = k·x
and get the answer:
y = x
hope this helped good luck! :)
