cos(x)=-1+2sin2(x)-2sin(x)cos(x)+sin(x)+1,
cos(x)=2sin2(x)-2sin(x)cos(x)+sin(x),
0=2sin2(x)-2sin(x)cos(x)+sin(x)-cos(x),
0=sin(x)(2sin(x)+1)-cos(x)(2sin(x)+1)=(sin(x)-cos(x))(2sin(x)+1).
Therefore, sin(x)=cos(x)⇒x=π/4 or sin(x)=-½, x=-π/6. That is, x=45° or -30°.