Question

Cos^4x-sin^4x=cos9x
Можно решение?)

Answer 1

   $cos^4x-sin^4x=cos9x\ (1-sin^2x)^2-sin^4x=cos9x\ 1-2sin^2x=cos9x\ cos2x=cos9x\ cos2x-cos9x=0\ sin(5.5x)*sin(3.5x)=0\ left { {{sin(5.5x)=0} atop {sin(3.5x)=0}} right. \ x=frac{2pi*n}{11}\ x=2pi*n\ x=2pi*n-frac{6pi}{7}\ x=2pi*n-frac{4pi}{7}\ x=2pi*n-frac{2pi}{7}\ x=2pi*n+frac{2pi}{7}$