cos(П+x)=sin П/2

sin5x cos4x - cos5x sin4x=1

cos alfa / 1-sin alfa = 1+sin alfa / cos alfa

1)cos(π+x)=sinπ/2-cosx=1cosx=-1x=π+2πn2)sin5xcos4x-cos5xsin4x=1sin(5x-4x)=1sinx=1x=π/2+2πn3)cosa/(1-sina)=(1+sina)/cosacos²a=(1-sina)(1+sina)cos²a=1-sin²acos²a=cos²a