Solve the equation (x+3)(x-3) = -9. What are the solutions to the equation if you replace x first with sinx and then with cosx, where 0≤x≤2pi?

Answer 1

x^2 - 9 = -9 ??
x^2 = 0

sin^2 x = 0
x = 0 or 180 degrees

cos^2 x = 0
x = 90 or 270 degrees