已知y=x/lnx是微分方程y'=y/x+φ(x/y)的解,则φ(x/y)的表达式是?A.-(y^2)/(x^2)B.(y^2)/(x^2)C.-(x^2)/(y^2)D.(x^2)/(y^2)

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已知y=x/lnx是微分方程y'=y/x+φ(x/y)的解,则φ(x/y)的表达式是?A.-(y^2)/(x^2)B.(y^2)/(x^2)C.-(x^2)/(y^2)D.(x^2)/(y^2)
已知y=x/lnx是微分方程y'=y/x+φ(x/y)的解,则φ(x/y)的表达式是?
A.-(y^2)/(x^2)
B.(y^2)/(x^2)
C.-(x^2)/(y^2)
D.(x^2)/(y^2)

已知y=x/lnx是微分方程y'=y/x+φ(x/y)的解,则φ(x/y)的表达式是?A.-(y^2)/(x^2)B.(y^2)/(x^2)C.-(x^2)/(y^2)D.(x^2)/(y^2)
你直接代进去不就是了吗..
y'=(lnx-1)/(lnx)^2
φ(x/y)=y'-y/x=(lnx-1)/(lnx)^2-1/lnx
=-1/(lnx)^2=-y^2/x^2
A

y = x/lnx
y' = (lnx - 1)/(lnx)^2
y'=y/x+φ(x/y)
(lnx - 1)/(lnx)^2 = (x/lnx)/x = φ(x/y)
φ(x/y) = (lnx - 1)/(lnx)^2 - 1/lnx
= -1/(lnx)^2
= -y^2/x^2