Question

cosx=(cos(x/2)-sin(x/2))^2-1

Answer 1

$cos(x) = (cos(frac{x}{2}) - sin(frac{x}{2}))^{2} - 1\ cos(x) = cos^{2}(frac{x}{2}) - 2sin(frac{x}{2})cos(frac{x}{2}) + sin^{2}(frac{x}{2}) - 1\ cos(x) = -sin(x) |:sin(x)\ ctg(x) = -1\ => x = frac{3pi}{4} + picdot n$