Cos5x- cos15x=ctg5x [2x-3]=4xпомогите а!?

cos5x-(4cos^3(5x)-3cos5x)=cos5x/sin5x; 4cos5x-4cos^3(5x)=cos5x/sin5x; 4cos5x(1-cos^2(5x))=cos5x/sin5x; 4(1-cos^2(5x))=1/sin5x; 4sin^2(5x)=1/sin5x; 4sin^3(5x)=1; sin^3(5x)=0.25; sin5x=(0.25)^(1/3); 5x=(-1)^n*arcsin(1/64)+Pi*n;neZ; x=((-1)^n*arcsin(1/64)+Pi*n)/5;neZ.