Question

1)cos*2 pi/8+ sin pi/8 cos pi/8 2) sin105sin75

Answer 1

 1)cos*2pi/8+sinpi/8cospi/8=cospi/4+1/2*2sinpi/8cospi/8=cospi/4+1/2sinpi/4=v2/2+1/2sinpi/4=v2/2+1/2v2/2=v2/2(1+1/2)=3/2*v2/2=3v2/4
2) sin105sin75=(cos(105-75)-cos(105+75))/2=(cos30-cos180)/2=(v3/2-(-1))/2=(v3/2+1)/2