题目内容
求证：tan（x+y）+tan（x-y）=
．
| sin2x |
| cos2x-sin2y |
证明：左=
+
=
=
=
=右．
| 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 |
=
| sin2x |
| cos2x-sin2y |
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