∫(2sinx+cosx)/(sinx+2cosx)dx

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∫(2sinx+cosx)/(sinx+2cosx)dx∫(2sinx+cosx)/(sinx+2cosx)dx∫(2sinx+cosx)/(sinx+2cosx)dx令cosx+2sinx=A(si

∫(2sinx+cosx)/(sinx+2cosx)dx
∫(2sinx+cosx)/(sinx+2cosx)dx

∫(2sinx+cosx)/(sinx+2cosx)dx
令 cosx + 2sinx = A(sinx + 2cosx) + B(cosx - 2sinx)
cosx + 2sinx = (2A + B)cosx + (A - 2B)sinx
2A + B = 1
A - 2B = 2
=> A = 4/5,B = -3/5
cosx + 2sinx = (4/5)(sinx + 2cosx) - (3/5)(cosx - 2sinx)
∫ (cosx + 2sinx)/(sinx + 2cosx) dx
= (4/5)∫ dx - (3/5)∫ (cosx - 2sinx)/(sinx + 2cosx) dx
= (4/5)x - (3/5)∫ d(sinx + 2cosx)/(sinx + 2cosx)
= (4/5)x - (3/5)ln|sinx + 2cosx| + C