Упростите выражение: sin(pi + a)*cos(pi-a) сtg((3pi/2) - a)

Question

Упростите выражение:

sin(pi + a)*cos(pi-a)

сtg((3pi/2) - a)

Answer 1

sin(pi + a)*cos(pi-a) = - sin a * (- cos a) = sin a * cos a

сtg((3pi/2) - a) = tg a

(sin a * cos a) / tg a = (sin a * cos a) / (sin a / cos a) = (sin a * cos a * cos a) / sin a = cos a * cos a = (cos a)^2