5 sin 11П/12 * cos 11П/12

5sin(11pi/12)*cos(11pi/12) = 5 sin(2*11pi/12)/2 = 5/2*sin(11pi/6) = = 5/2*sin(2pi - pi/6)= -5/2*sin(pi/6) =-5/2*1/2 = -1,25