※ 引述《Roseinmymind (不想要慈悲者的憐憫)》之銘言：
: y'x^2+xy=1 ifx>0 and y(1)=2
y' + (1/x)y = 1/x^2 ... (1)
積分因子 : exp[∫(1/x)dx] = x
(1)乘x 得
xy' + y = 1/x ===> (xy)' = 1/x ===> ∫(xy)dx = ∫1/x
∴ y = (lnx)/x + C
y(1) = 2 ∴ C = 2
y = (lnx)/x + 2 #
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