试题与答案

计算:(1)2cos55°-3sin5°cos5°;(2)1+2sin290°c

题型:解答题

题目:

计算:
(1)
2cos55°-
3
sin5°
cos5°

(2)
1+2sin290°cos430°
sin250°+cos790°

答案:

(1)原式=

2sin35°-
3
sin5°
cos5°
=
2sin(30°+5°)-
3
sin5°
cos5°
=
cos5°+
3
sin5°-
3
sin5°
cos5°
=1.

(2)原式=

1-2sin70°cos70°
-sin70°+cos70°
=
|sin70°-cos70°|
-sin70°+cos70°
=-1.

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