cos(π/4+a)=3/5所以cos(π/2+2a)=2[cos(π/4+a)]^2-1=2*9/25-1-sin2a=-7/25sin2a=7/25cos(π/4+a)=cosa*√2/2-sin*√2/2=3/5cosa-sina=3√2/5两边平方2sinacosa=sin2a=7/25所以(sina+cosa)^2=1+2sinacosa=32/25a在...