问题 解答题
计算:
sin65°+sin15°sin10°
sin25°-cos15°cos80°
答案

sin65°+sin15°sin10°
sin25°-cos15°cos80°
=
cos(10°+15°)+sin15°sin10°
sin(15°+10°)-cos15°sin10°
=
cos10°cos15°
sin15°cos10°
 

=

cos15°
sin15°
=
cos(45°-30°)
sin(45°-30°)
=
2
2
×
3
2
+
2
2
×
1
2
2
2
×
3
2
-
2
2
×
1
2
=
6
+
2
6
-
2
=2+
3

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