因为cos²(π/4-x)= cos²[π/2- (π/4+x)]= sin²(π/4+x)所以2cot(π/4+x)cos²(π/4-x)=2cot(π/4+x) sin²(π/4+x)=2cos(π/4+x) sin(π/4+x)= sin[2(π/4+x)]= sin(π/2+2x)= cos2x∴cos2x...