cos(45°-α)等于什么,是cosα?还是什么?
来源:学生作业帮 编辑:搜搜做题作业网作业帮 分类:数学作业 时间:2024/08/17 03:14:17
cos(45°-α)等于什么,是cosα?还是什么?
其实这道题是这样的求2sin14°cos31°+sin17°等于多少,
其实这道题是这样的求2sin14°cos31°+sin17°等于多少,
![cos(45°-α)等于什么,是cosα?还是什么?](/uploads/image/z/19683892-28-2.jpg?t=cos%2845%C2%B0-%CE%B1%29%E7%AD%89%E4%BA%8E%E4%BB%80%E4%B9%88%2C%E6%98%AFcos%CE%B1%3F%E8%BF%98%E6%98%AF%E4%BB%80%E4%B9%88%3F)
2sin14°cos31°+sin17°
=2sin14(cos14cos17-sin14sin17)+sin17
=2sin14cos14cos17-2sin14sin14sin17+sin17
=sin28cos17+sin17(1-2sin14sin14)
=sin28cos17+sin17cos28
=sin45=根号2/2
=2sin14(cos14cos17-sin14sin17)+sin17
=2sin14cos14cos17-2sin14sin14sin17+sin17
=sin28cos17+sin17(1-2sin14sin14)
=sin28cos17+sin17cos28
=sin45=根号2/2