If you would like to know the value of b^2 - 4 a c, you can calculate this using the following steps:
x (x + 8) = 9
x^2 + 8x - 9 = 0
ax^2 + bx + c = 0
a = 1
b = 8
c = - 9
D = b^2 - 4 a c = 8^2 - 4 1 (-9) = 64 + 4 9 = 64 + 36 = 100
The correct result would be 100.
