sin(π/4+α)=√2/2(sina+cosa)=1/3 平方1/2(1+sin2a)=1/9 sin2a=-7/9cos(π/2-2α)= sin2a=-7/9
cos(π/2-2α)=cos(π-π/2-2α)=cos[π-(π/2+2α)]=-cos(π/2+2α)=-[1-2sin²(π/4+α)]=-[1-2*(1/3)²]=-[1-2/9]=-7/9
