问题
解答题
求证：tan（x+y）+tan（x-y）=
|
答案
证明：左=
+sin(x+y) cos(x+y) sin(x-y) cos(x-y)
=sin[(x+y)+(x-y)] cos2x•cos2y-sin2x•sin2y
=sin2x cos2x-(cos2x+sin2x)sin2y
=
=右．sin2x cos2x-sin2y
搜题请搜索小程序“爱下问搜题”
求证：tan（x+y）+tan（x-y）=
|
证明：左=
+sin(x+y) cos(x+y) sin(x-y) cos(x-y)
=sin[(x+y)+(x-y)] cos2x•cos2y-sin2x•sin2y
=sin2x cos2x-(cos2x+sin2x)sin2y
=
=右．sin2x cos2x-sin2y