题目有歧义,若是 y' = (x+y)/(x-y), 则为齐次方程,
令 y = px, 则 p+xdp/dx = (1+p)/(1-p)
xdp/dx = (1+p^2)/(1-p)
(1-p)dp/(1+p^2) = dx/x
arctanp - (1/2)ln(1+p^2) = lnx + (1/2)lnC
2arctanp = ln(1+p^2) + 2lnx + lnC
Cx^2(1+p^2) = e^(2arctanp)
通解 C(x^2+y^2) = e^[2arctan(y/x)]
y(1) = 1 代入,得 C = (1/2)e^(π/2)
则 (1/2)e^(π/2)(x^2+y^2) = e^[2arctan(y/x)]
特解条件不全,
无法给出特解,
只能给出通解,
具体解答如图所示。
方法如下所示。
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