已知sin2α=2/3 则cos^2(α+π/4)我们上课记的:cos[2(α+π/4)]=cos(2α+π/2)=-sin2α=-2/3又 cos[2(α+π/4)]=2cos^2(α+π/4)-1-2/3=2cos^2(α+π/4)-1cos^2(α+π/4)=1/6谁能给我讲下思路啊?看不懂
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![已知sin2α=2/3 则cos^2(α+π/4)我们上课记的:cos[2(α+π/4)]=cos(2α+π/2)=-sin2α=-2/3又 cos[2(α+π/4)]=2cos^2(α+π/4)-1-2/3=2cos^2(α+π/4)-1cos^2(α+π/4)=1/6谁能给我讲下思路啊?看不懂](/uploads/image/z/10048952-56-2.jpg?t=%E5%B7%B2%E7%9F%A5sin2%CE%B1%3D2%2F3+%E5%88%99cos%5E2%28%CE%B1%2B%CF%80%2F4%29%E6%88%91%E4%BB%AC%E4%B8%8A%E8%AF%BE%E8%AE%B0%E7%9A%84%EF%BC%9Acos%5B2%EF%BC%88%CE%B1%2B%CF%80%2F4%EF%BC%89%5D%3Dcos%EF%BC%882%CE%B1%2B%CF%80%2F2%EF%BC%89%3D-sin2%CE%B1%3D-2%2F3%E5%8F%88+cos%5B2%EF%BC%88%CE%B1%2B%CF%80%2F4%EF%BC%89%5D%3D2cos%5E2%EF%BC%88%CE%B1%2B%CF%80%2F4%EF%BC%89-1-2%2F3%3D2cos%5E2%EF%BC%88%CE%B1%2B%CF%80%2F4%EF%BC%89-1cos%5E2%EF%BC%88%CE%B1%2B%CF%80%2F4%EF%BC%89%3D1%2F6%E8%B0%81%E8%83%BD%E7%BB%99%E6%88%91%E8%AE%B2%E4%B8%8B%E6%80%9D%E8%B7%AF%E5%95%8A%3F%E7%9C%8B%E4%B8%8D%E6%87%82)
已知sin2α=2/3 则cos^2(α+π/4)我们上课记的:cos[2(α+π/4)]=cos(2α+π/2)=-sin2α=-2/3又 cos[2(α+π/4)]=2cos^2(α+π/4)-1-2/3=2cos^2(α+π/4)-1cos^2(α+π/4)=1/6谁能给我讲下思路啊?看不懂
已知sin2α=2/3 则cos^2(α+π/4)
我们上课记的:cos[2(α+π/4)]
=cos(2α+π/2)
=-sin2α
=-2/3
又 cos[2(α+π/4)]
=2cos^2(α+π/4)-1
-2/3=2cos^2(α+π/4)-1
cos^2(α+π/4)=1/6
谁能给我讲下思路啊?看不懂
已知sin2α=2/3 则cos^2(α+π/4)我们上课记的:cos[2(α+π/4)]=cos(2α+π/2)=-sin2α=-2/3又 cos[2(α+π/4)]=2cos^2(α+π/4)-1-2/3=2cos^2(α+π/4)-1cos^2(α+π/4)=1/6谁能给我讲下思路啊?看不懂
用cos二倍角公式 cos2A=2(cosA)平方-1
它只是类似知道答案反推的写法
cos²(α+π/4)?
=(1+cos(2a+π/2)/2
=(1-sin2a)/2
=1/3/2
=1/6
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