sin(a+pai/4)=3/5,求sin(a+3pai/4)/cos(pai/4+a)

Question

sin(a+pai/4)=3/5,求sin(a+3pai/4)/cos(pai/4+a)

Answer 1

sin(a+3π/4)=sin[π/2+(a+π/4)]=cos(a+π/4)
所以,原式=cos²(a+π/4)
=1-sin²(a+π/4)
=16/25