两边同时乘以2 然后2y=2cos^2(x/2-7π/8)-2cos^2(x/2+7π/8=1-2cos^2(x/2-7π/8)-[1-2cos^2(x/2+7π/8]=cos(x-7π/4)-cos(x+7π/4)令T=x-7π/4 x=T+7π/4所以2y=cosT-cos(x+7π/2)=cosT+sinT=√2sin(T+π/4）所以y的...