Найдите значение выражения - 30 / (сos^2 87 + cos^2 177)

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