问题
解答题
求证：tan2x+
|
答案
证明：左边=
+sin2x cos2x cos2x sin2x
=sin4x+cos4x sin2xcos2x
=(sin2x+cos2x)2-2sin2xcos2x
sin22x1 4
=
=8-4sin22x 1-cos4x 4+4cos22x 1-cos4x
=
=4+2(1+cos4x) 1-cos4x 2(3+cos4x) 1-cos4x
=右边．
∴tan2x+
=1 tan2x
．2(3+cos4x) 1-cos4x