化简:cos^2(二分之A-八分之7派)-cos^2(二分之A+八分之7派)_数学解答

化简:cos^2(二分之A-八分之7派)-cos^2(二分之A+八分之7派)

人气：298 ℃　时间：2020-05-02 23:46:52

解答

cos²(A/2-7π/8)-cos²(A/2+7π/8)
=1/2[1+cos(A-7π/4)-1-cos(A-7π/4)]
=1/2[cos(A-7π/4)-cos(A-7π/4)]
=sinAsin(7π/4)
=-√2sinA/2