已知tan(π+α)=-2/1,求下列各式的值(1)[2cos(π-α)-3sin(π+α)]/[4cos(α-2π)+sin(4π-α)](2)sin(α-2π)xcos(α+5π)

Question

已知tan (π+ α)=-2/1,求下列各式的值
(1)[2cos(π-α)-3sin(π+α)]/[4cos(α-2π)+sin(4π-α)]
(2)sin(α-2π)xcos(α+5π)

Answer 1

tan(pai+alpha) = -2,tan(alpha) = -2,alpha 在第二象限
cos(pai-alpha) = -cos(alpha) = 1/根号（5）,sin(pai+alpha) = -sin(alpha) =-2/根号（5）
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