来自焦扬的问题
设函数f(u)具有二阶连续导数,z=f(excosy)满足∂2z∂x2+∂2z∂y2=(4z+excosy)e2x.若f(0)=0,f′(0)=0,求f(u)的表达式.
设函数f(u)具有二阶连续导数,z=f(excosy)满足∂2z∂x2+∂2z∂y2=(4z+excosy)e2x.若f(0)=0,f′(0)=0,求f(u)的表达式.


设函数f(u)具有二阶连续导数,z=f(excosy)满足∂2z∂x2+∂2z∂y2=(4z+excosy)e2x.若f(0)=0,f′(0)=0,求f(u)的表达式.
设函数f(u)具有二阶连续导数,z=f(excosy)满足∂2z∂x2+∂2z∂y2=(4z+excosy)e2x.若f(0)=0,f′(0)=0,求f(u)的表达式.
设u=excosy,则z=f(u)=f(excosy),∂z∂x=f’(u)excosy,∂2z∂x2=f’’(u)e2xcos2y+f’(u)excosy∂z∂y=−f’(u)exsiny,∂2z∂y2=f’’(u)e2xsin2y−f’(u)excosy所以:∂2z∂x2+∂2z∂y2=f’’(u)e2x=f...