左边=[sin²(a/2)+cos²(a/2)+2sin(a/2)cos(a/2)]/[cos²(a/2)-sin²(a/2)]=[sin(a/2)+cos(a/2)]²/[sin(a/2)+cos(a/2)][sin(a/2)-cos(a/2)]=[sin(a/2)+cos(a/2)]/[sin(a/2)-cos(a/2)]上下除以c...