cos(π/4-a)*cos(π/4+a)=1/8即：(√2/2*cosa+√2/2*sina)(√2/2*cosa-√2/2*sina)=1/8即得：(cosa)^2-(sina)^2=1/4联合 (cosa)^2+(sina)^2=1解得：(sinx)^2=3/8(cosa)^2=5/8所以：(sina)^4+(cosa)^4= 17/32...