ä¹ç§¯ç导æ°å
¬å¼ï¼(uv)' = u'v + uv'ï¼
两边ä¹ä»¥ e^-xï¼å¾ e^-x * f ''(x) - e^-x * f(x) = 0ï¼
å为 e^-x * [f '(x)] ' + (e^-x) ' * f(x) = 0ï¼
åå以 e^-x * f '(x) - e^-x * f '(x)ï¼å°±æ¯
e^-x * [f '(x) + f(x)] ' + (e^-x) ' * [f(x)+f '(x)] = 0ï¼
ä¸å¼å·¦è¾¹å°±æ¯ e^-x * [f '(x)+f(x)] ç导æ°ã
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