已知sinα=3/5,α∈(π/2,π)求sin(α-π/4).cos(α+π/3)及tan2π的值
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已知sinα=3/5,α∈(π/2,π)求sin(α-π/4).cos(α+π/3)及tan2π的值
已知sinα=3/5,α∈(π/2,π)求sin(α-π/4).cos(α+π/3)及tan2π的值
已知sinα=3/5,α∈(π/2,π)求sin(α-π/4).cos(α+π/3)及tan2π的值
sinα=3/5,α∈(π/2,π)
得:cosα=-4/5 tanα=-3/4
sin(α-π/4)=sinαcosπ/4-sinπ/4cosα=(7√2)/10
cos(α+π/3)=cosαcosπ/3-sinαsinπ/3=(-4-3√3)/10
tan2α=(-2*3/4)/(1-(-3/4)^2)=-24/7
sinα=3/5,α∈(π/2,π),所以cosα=-4/5
sin(α-π/4)=sinα*cos(π/4)-cosα*sin(π/4)=....
同理,可以求出cos(α+π/3)
公式为cos(a+b)=cosa*cosb-sina*sinb
最后tan2π=0