已知cos((π/4)-x)=-3/5,求sin2x/(sin(x+π/4))的值.求过程sin(x+π/4)=cos(π/4-x)=-3/5怎么得出来的啊?
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![已知cos((π/4)-x)=-3/5,求sin2x/(sin(x+π/4))的值.求过程sin(x+π/4)=cos(π/4-x)=-3/5怎么得出来的啊?](/uploads/image/z/1105110-54-0.jpg?t=%E5%B7%B2%E7%9F%A5cos%EF%BC%88%EF%BC%88%CF%80%2F4%EF%BC%89-x%EF%BC%89%3D-3%2F5%2C%E6%B1%82sin2x%2F%EF%BC%88sin%EF%BC%88x%2B%CF%80%2F4%EF%BC%89%EF%BC%89%E7%9A%84%E5%80%BC.%E6%B1%82%E8%BF%87%E7%A8%8Bsin%28x%EF%BC%8B%CF%80%2F4%29%3Dcos%28%CF%80%2F4%EF%BC%8Dx%29%3D%EF%BC%8D3%2F5%E6%80%8E%E4%B9%88%E5%BE%97%E5%87%BA%E6%9D%A5%E7%9A%84%E5%95%8A%EF%BC%9F)
已知cos((π/4)-x)=-3/5,求sin2x/(sin(x+π/4))的值.求过程sin(x+π/4)=cos(π/4-x)=-3/5怎么得出来的啊?
已知cos((π/4)-x)=-3/5,求sin2x/(sin(x+π/4))的值.求过程
sin(x+π/4)=cos(π/4-x)=-3/5怎么得出来的啊?
已知cos((π/4)-x)=-3/5,求sin2x/(sin(x+π/4))的值.求过程sin(x+π/4)=cos(π/4-x)=-3/5怎么得出来的啊?
cos[(π/4)-x]=sin{(π/2)-[(π/4)-x]}=sin[(π/4)+x]=-3/5
∴sin[(π/4)+x]=-3/5
sin2x=cos[(π/2)-2x]=cos2[(π/4)-x]=2*{cos[(π/4)-x]}^2-1=2*(9/25)-1=-7/25
sin2x/(sin(x+π/4))= 7/15
sin(a)=cos(π/2-a)
则:
sin(x+π/4)=cos[(π/2)-(x+π/4)]=cos(π/4-x)
sin(x+π/4)=cos(π/4-x)=-3/5
另外,
sin2x=cos(π/2-2x)=cos[2(π/4-x)] 【二倍角展开】
=2cos²(π/4-x)-1
=2×(-...
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sin(a)=cos(π/2-a)
则:
sin(x+π/4)=cos[(π/2)-(x+π/4)]=cos(π/4-x)
sin(x+π/4)=cos(π/4-x)=-3/5
另外,
sin2x=cos(π/2-2x)=cos[2(π/4-x)] 【二倍角展开】
=2cos²(π/4-x)-1
=2×(-3/5)²-1
=-7/25
则:[sin2x]/[sin(x+π/4)]=[-3/5]/[-7/25]=15/7
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