Споминаем тригонометрию
1) 10V(6)cos(-pi/4)*sin(-pi/3) = -10V(6)*V(2)/2*V(3)/2 = -10V(6)*V(6)/4 = -15
2) 28sin 68/sin 292 = 28sin 68/sin(360-68) = -28sin 68/sin 68 = -28
3) 16cos 128/cos 52 = 16cos(180-52)/cos 52 = 16cos 52/cos 52 = 16
4) -19tg 3/tg 177 = -19tg 3/tg(180-3) = -19tg 3/(-tg 3) = 19
5) 21sin 408/sin 48 = 21sin(360+48)/sin 48 = 21sin 48/sin 48 = 21
6) 4tg 74*tg 164 = 4tg 74*tg(90+74) = 4tg 74*(-ctg 74) = -4
7) 38tg 10*tg 80 = 38tg 10*tg(90-10) = 38tg 10*ctg 10 = 38
8) -30/(sin^2 87 + sin^2 177) = -30/(sin^2 87 + sin^2(90+87)) =
= -30/(sin^2 87 + cos^2 87) = -30
9) 23/(cos^2 56 + cos^2 146) = 23/(cos^2 56 + cos^2(90+56)) =
= 23/(cos^2 56 + sin^2 56) = 23