You actually need two (x,y) points to figure out the equation. Suppose you are given the points (1,6) and (3,54). Here are the steps.
1) Plug in both points:
y = abx
6 = ab1
54 = ab3
2) To find the value of b, take the ratio of the two:
54/6 = ab3/ab1
9 = b2
3 = b
So your equation so far is y = a·3x
3) To find the value of a, plug in one of the two points and solve for a:
y = a·3x
Plug in (1,6)
6 = a·31
2 = a
The final equation is y = 2·3x
Ellie V.
Thank you so much.04/16/19