三角的计算求值(1).sin7°+cos15°sin8°-----------------------cos7°+sin
来源:学生作业帮 编辑:神马作文网作业帮 分类:数学作业 时间:2024/09/20 23:46:59
三角的计算求值
(1).sin7°+cos15°sin8°
-----------------------
cos7°+sin15°sin8°
(2)2cos10°-sin20°
---------------------
cos20°
(1).sin7°+cos15°sin8°
-----------------------
cos7°+sin15°sin8°
(2)2cos10°-sin20°
---------------------
cos20°
(1)sin(15-8)+cos15sin8/(cos(15-8)+sin15sin8)
=sin15cos8-cos15sin8+cos15sin8/cos15cos8+sin15sin8-sin15sin8
=sin15cos8/cos15sin8
=tan15
(2)sin20=sin(30-10)
所以 (2cos10°—sin20°)/sin70°
=(2cos10°—sin(30-10))/sin70°
=(2cos10-(sin30cos10-cos30sin10))/sin70
=(2cos10-1/2cos10+根号3/2sin10)/sin70
=(3/2sin10+根号3/2sin10)/sin70
=根号3(根号3/2cos10+1/2sin10)/sin70
=根号3sin(10+60)/sin70
=根号3
第一题分母可能是减 否则无法化简
=sin15cos8-cos15sin8+cos15sin8/cos15cos8+sin15sin8-sin15sin8
=sin15cos8/cos15sin8
=tan15
(2)sin20=sin(30-10)
所以 (2cos10°—sin20°)/sin70°
=(2cos10°—sin(30-10))/sin70°
=(2cos10-(sin30cos10-cos30sin10))/sin70
=(2cos10-1/2cos10+根号3/2sin10)/sin70
=(3/2sin10+根号3/2sin10)/sin70
=根号3(根号3/2cos10+1/2sin10)/sin70
=根号3sin(10+60)/sin70
=根号3
第一题分母可能是减 否则无法化简
1.sin7°+cos15°sin8°/cos7°-sin15°cos8°=
(sin7°+cos15°cos8°)/(sin7°-sin15°sin8°)的化简
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