Question

C 1-9 с решение плиз !!!!

Answer 1

1
2cos²a-1=2/3
cos²a=(1+2/3):2=5/3*1/2=5/6
2
cos²a=1-1/16=15/16
5cos²a-1=75/16-1=59/16
3
cos(54-9)=cos45=√2/2
4
sin(2π/5-π/15)=cosπ/3=√3/2
5
cos60+sin60=1/2+√3/2=(1+√3)/2
6
(cos²a/sin²a  -1)/(cos²a-sin²a)=(cos²a-sin²a)/sina(cos²a-sin²a)-1/sin²a
7
-sin45+sin45=0
8
cos²a+2cosasina+sin²a+2sinacosa=1+4sinacosa=1+2sin2a
9
7sin(3π/2-x)=-7cosx=2⇒7cosx=-2
7cos(2x-x)=7cosx=-2