Question

дано: cos2a = -1/2, p<2a<3p/2 вычислите 2sina - cosa

Answer 1

cos2a=1/8
cos²a=(1+cos2a)/2=(1+1/8)/2=9/8:2=9/16⇒cosa=3/4
sina=-√1-9/16=-√7/4
2sina+3cosa=-2√7/4+9/4=(-2√7+9)/4