sin(π/4+2a)sin(π/4-2a)=sin[π/2-(π/4-2a)]sin(π/4-2a)=cos(π/4-2a)sin(π/4-2a)=[cos(4a)]/2=1/4 ==>cos(4a)=1/2,因为a属于（π/4,π/2）,所以4a属于（π,2π）,所以4a=5π/3,所以a=5π/12所以2（sina）^2+ta...