Question 818899
Cosx=-sinx
sqrt(1-sin^2(x)) = -sin(x)
1 - sin^2 = sin^2
sin^2 = 1/2
sin = sqrt(2)/2
x = pi/4 + n*2pi, n = 0,1,2,3...
x = 3pi/4 + n*2pi, n = 0,1,2,3...