4.7 8 sin 120° cos 240° sin 150° sin 780°

sin(120°) = sin(180°-60°) = sin(60°) = √3/2; cos(240°) = cos(180°+60°) = -cos(60°) = -1/2; sin(150°) = sin(180°-30°) = sin(30°) = 1/2; sin(780°) = sin(780°-2*360°) = sin(60°) = √3/2. 8 * (√3/2) * (-1/2) * (1/2) * (√3/2) = 8 * (-3/16) = -1.5