大一高等数学微分方程求解
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若是 e^n, 则化为 y' - xy = xe^n 是一阶线性微分方程
y = e^(∫xdx) [ C + e^n∫xe^(∫-xdx)dx ]
= e^(x^2/2) [ C + e^n∫xe^(-x^2/2)dx ]
= e^(x^2/2) [ C - e^n∫e^(-x^2/2)d(-x^2/2) ]
= e^(x^2/2) [ C - e^ne^(-x^2/2) ]
= Ce^(x^2/2) - e^n
若是 e^x, 则化为 y' - xy = xe^x 是一阶线性微分方程
y = e^(∫xdx) [ C + ∫xe^xe^(∫-xdx)dx ]
= e^(x^2/2) [ C + ∫xe^xe^(-x^2/2)dx ]
= e^(x^2/2) [ C - ∫e^xe^(-x^2/2)d(-x^2/2) ]
= e^(x^2/2) [ C - ∫e^xde^(-x^2/2) ]
= e^(x^2/2) [ C - e^(x-x^2/2) + ∫e^(-x^2/2)e^xdx ]
不能用初等函数表示
y = e^(∫xdx) [ C + e^n∫xe^(∫-xdx)dx ]
= e^(x^2/2) [ C + e^n∫xe^(-x^2/2)dx ]
= e^(x^2/2) [ C - e^n∫e^(-x^2/2)d(-x^2/2) ]
= e^(x^2/2) [ C - e^ne^(-x^2/2) ]
= Ce^(x^2/2) - e^n
若是 e^x, 则化为 y' - xy = xe^x 是一阶线性微分方程
y = e^(∫xdx) [ C + ∫xe^xe^(∫-xdx)dx ]
= e^(x^2/2) [ C + ∫xe^xe^(-x^2/2)dx ]
= e^(x^2/2) [ C - ∫e^xe^(-x^2/2)d(-x^2/2) ]
= e^(x^2/2) [ C - ∫e^xde^(-x^2/2) ]
= e^(x^2/2) [ C - e^(x-x^2/2) + ∫e^(-x^2/2)e^xdx ]
不能用初等函数表示
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