Given points(-2,-25),(1,-4),(3,-10) find the equation.

First i put the points into y=ax^2+bx=c form getting:

A: 4a-2b+c= -25

B: a+b+c= -4

C: 9a+3b+c= -10

then I solve for A:+B: and get D: 3a-3b= -21

then I go to solve for A:+C; and get E: -5a-5b= -15

then I try to solve D:+E: and get to 15a-15b= -105

.................................................-15a -15b= 75

what do i do if the a and b variables both cancel out?