zx=f'(e^xcosy)*e^xcosy zxx=f''(e^xcosy)(e^xcosy)^2+f'(e^xcosy)*e^xcosy zy=f'(e^xcosy)*e^x(-siny) zyy=f''(e^xcosy)*[e^x(-siny)]^2+f'(e^xcosy)*e^x(-cosy) zxx+zyy=f''(e^xcosy)(e^xcosy)^2+f'(e^xcosy)*e^xcosy+f''(e^xcosy)*[e^x(siny)]^2-f'(e^xcosy)*e^xcosy =f''(e^xcosy)e^(2x) =4[f(e^xcosy)+e^xcosy]e^(2x) f''(u)=4f(u)+4u f''-4f=4u é½æ¬¡è§£ï¼r^2-4=0 r=-2,2 f=Ae^(2u)+Be^(-2u) éé½æ¬¡è§£ï¼f=-u å 为å³ç«¯æ¯ä¸æ¬¡å½æ° f=Ae^(2u)+Be^(-2u)-u u=0,f=A+B=0 f'=2Ae^(2u)-2Be^(-2u)-1 u=0,f'=2A-2B-1=0 A=1/4,B=-1/4 æ以 f(u)=(1/4)e^(2u)-(1/4)e^(-2u)-u
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