Question

найдите 4cos2a если sin а= -0,5

Answer 1

 

4Cos2a = 4( 1-2(Sina)^{2})=4-8*1/4=4-2=2

Answer 2

cos2a = cos² a - sin ² а

 

cos a = ±√(1-sin ² а) = ±√ (1-¼) = ± √3/2

 

 

cos2a = ¾ - ¼ = ½

4cos2a = 4 · ½ =2