已知f(x)=4sin(3x+π/4),若f(2/3a+π/12)=12/5,求sina的值
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![已知f(x)=4sin(3x+π/4),若f(2/3a+π/12)=12/5,求sina的值](/uploads/image/z/12874183-7-3.jpg?t=%E5%B7%B2%E7%9F%A5f%EF%BC%88x%EF%BC%89%3D4sin%EF%BC%883x%2B%CF%80%2F4%EF%BC%89%2C%E8%8B%A5f%EF%BC%882%2F3a%2B%CF%80%2F12%EF%BC%89%3D12%2F5%2C%E6%B1%82sina%E7%9A%84%E5%80%BC)
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已知f(x)=4sin(3x+π/4),若f(2/3a+π/12)=12/5,求sina的值
已知f(x)=4sin(3x+π/4),若f(2/3a+π/12)=12/5,求sina的值
已知f(x)=4sin(3x+π/4),若f(2/3a+π/12)=12/5,求sina的值
【解】f(2/3a+π/12)=12/5
==>4sin[3(2/3a+π/12)+π/4)]=12/5
==>4sin(a+π/4+π/4)=12/5
==>4sin(a+π/2)=12/5
==>-4sina=12/5
==>sina=-3/5
就打入进去就行了。4sin(2a+π/2)=12/5
-4cos 2a=12/5