My solutions to 16(c), which probably make a whole lot more sense because its JUST quadratic formula...
You eventually derive
y^2 + (1 - 2c)y + (c^2 - r^2) = 0 after substituting x = y^2
Now, y = (2c - 1 +-sqrt(1 - 4c + 4c^2 - 4c^2 + 4r^2 ))/2
-> y = (2c - 1 +-sqrt(1 - 4c + 4r^2))/2
Knowing...