Представьте в виде произведения cos2t-cos4t-cos6t+cos8t

cos2t-cos4t-cos6t+cos8t=(cos2t+cos8t) — (cos 4t+cos6t)=2cos (2t+8t) /2*cos (2t-8t) /2-2cos (4t+6t) /2*cos (4t-6t) /2=2cos5t*cos3t-2cos5t*cost=2cos5t (cos3t-cost)=-4cos5t*sin (3t+t) /2*sin (3t-t) /2=-4cos5t*sin2t*sint