The equation of a circle A(x^2+y^2)+Bx+Cy+9=0 that passes through (1,0), (2,-1) and (8,7). Find B.

Question

Thanks!

Answer 1

what's the problem?
Plug in the coordinates and see what falls out.

A(1+0) + B(1) + C(0) + 9 = 0
A(4+1) + B(2) + C(-1) + 9 = 0
A(64+49) + B(8) + C(7) + 9 = 0

A + B = -9
5A + 2B - C = -9
113A + 8B + 7C = -9

A = 1
B = -10
C = -6