Re: [理工] [工數] ODE 請神人看一下...櫃求
※ 引述《topee (eason)》之銘言：
: ※ 引述《himanbobo (I have a dream)》之銘言：
: : dy/dx = 2x^2 + y/x
: : => xdy = 2x^3 dx + y dx
: : => xdy-ydx = 2x^3 dx
: : => (x^2)*d(y/x) = 2x^3 dx
: : => d(y/x) = 2xdx
: : => y/x = x^2 + c
: : => y = x^3 + cx
: : 代入Initial condition:
: : 5 = 1 + c ===> c = 4
: : 所以 y = x^3 + 4x
: y
: 大大我題目打錯了 是y'=3x^2 + ---
: x
dy y
------ = 3x^2 - ---- 萬一是負的?
dx x
y
dy = 3x^2 dx - --- dx
x
xdy + ydx = 3x^3 dx
d(xy) = 3x^3 dx
3
xy = ---x^4 + c
4
c = 17 /4 這樣對嗎?
--
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