题目内容
| sin(-250°)cos70° |
| cos2155°-sin225° |
A．-
| B．-
| C．
| D．
|
因为
=
=
=
=
=
=
=
．
故选C．
| sin(-250°)cos70° |
| cos2155°-sin225° |
=
| -sin250°cos70° |
| cos225°-sin225° |
=
| -sin(180°+70°)cos70° |
| cos225°-sin225° |
=
| sin70°cos70° |
| cos 50° |
=
| sin140° |
| 2cos 50° |
=
| sin40° |
| 2cos 50° |
=
| cos50° |
| 2cos 50° |
=
| 1 |
| 2 |
故选C．
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