1
sin²(π+π/8-a)-sin(2π-π/8+a)=sin²(π/8-a)-sin²(a-π/8)=
=sin²(π/8-a)-sin²(π/8-a)=0
2
cos²(3π/8-a)-cos²(π+3π/8+a)=cos²(3π/8-a)-cos²(3π/8+a)=
=1/2*(1+cos(3π/4-2a)-1-cos(3π/4+2a))=
=1/2(cos(π-π/4-2a)-cos(π-π/4+2a))=1/2(-cos(π/4+2a)+cos(2a-π/4))=
=1/2*(-2sin0*sin2a=0