一二题怎么写【数学】要过程
来源:学生作业帮 编辑:百度作业网作业帮 分类:数学作业 时间:2024/06/23 14:48:11
一二题怎么写【数学】要过程
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![](http://img.wesiedu.com/upload/b/3a/b3a967f6363561f4cd085e424a95ac99.jpg)
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![](http://img.wesiedu.com/upload/b/3a/b3a967f6363561f4cd085e424a95ac99.jpg)
![一二题怎么写【数学】要过程](/uploads/image/z/4167624-48-4.jpg?t=%E4%B8%80%E4%BA%8C%E9%A2%98%E6%80%8E%E4%B9%88%E5%86%99%E3%80%90%E6%95%B0%E5%AD%A6%E3%80%91%E8%A6%81%E8%BF%87%E7%A8%8B)
图片好模糊啊!不过还是给你解答一下吧,
1.cos(α+π/4)=cos(α)sin(π/4)-sin(α)cos(π/4)={cos(α)-sin(α)}sqrt(2)/2
α∈(3π/2,2π),cos(α)=12/13→sin(α)=-5/13(典型的勾股三角形5.12.13)
→cos(α+π/4)=17sqrt(2)/26,选择C.
2.sin(α+β)=sin(α)cos(β)+cos(α)sin(β),
sin(α)=2sqrt(5)/5→cos(α)=sqrt(5)/5
→sin(α+β)=2cos(β)sqrt(5)/5 + sin(β)sqrt(5)/5=3/5 ①
cos(β)^2+ sin(β)^2=1 ②
由①②→cos(β)=2sqrt(5)/5或2sqrt(5)/25,选择C
1.cos(α+π/4)=cos(α)sin(π/4)-sin(α)cos(π/4)={cos(α)-sin(α)}sqrt(2)/2
α∈(3π/2,2π),cos(α)=12/13→sin(α)=-5/13(典型的勾股三角形5.12.13)
→cos(α+π/4)=17sqrt(2)/26,选择C.
2.sin(α+β)=sin(α)cos(β)+cos(α)sin(β),
sin(α)=2sqrt(5)/5→cos(α)=sqrt(5)/5
→sin(α+β)=2cos(β)sqrt(5)/5 + sin(β)sqrt(5)/5=3/5 ①
cos(β)^2+ sin(β)^2=1 ②
由①②→cos(β)=2sqrt(5)/5或2sqrt(5)/25,选择C