Question

Пожалуйста помогите решить 4 и 1, ОЧЕНЬ СРОЧНО, ПОМОГИТЕ!!

Answer 1

4)cos²a-cos²(π/2 -a)=cos²a-sin²a=cos2a
1)sin7x+sin3x=cos2x
  2sin(7x+3x)/2*cos(7x-3x)/2=cos2x
 2sin5x*cos2x-cos2x=0
cos2x(2sin5x-1)=0
cos2x=0                                 2sin5x-1=0
2x=π/2+πn, n∈Z                    2sin5x=1
x=π/4+πn/2, n∈Z                   sin5x=1/2
                                               5x=(-1)^n *π/6 + πn,n∈Z
                                               x=(-1)^n*π/30 +πn/5, n∈Z
                                          
sin2x+sin2x=0
2sin2x=0|:2
sin2x=0
2x=πn, n∈Z
x=πn/2, n∈Z