设f(x,y)二阶连续可偏导,f’x(x,1)=2x+1一sinx,f"xy(x,y)=2x+2y,且f(0,y)=2y+3,则f(x,y)=________.

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问题 设f(x,y)二阶连续可偏导,f’x(x,1)=2x+1一sinx,f"xy(x,y)=2x+2y,且f(0,y)=2y+3,则f(x,y)=________.

选项

答案x2y+xy2+cosx+2y+2

解析 由f"(x,y)=2x+2y得
    f’(x,Y)=2xy+y2+ψ(z),
由f’(x,1)=2x+1一sinx得ψ(x)=一sinx,
即f’(x,Y)=2xy+y2一sinx,
由f’(x,y)=2xy+y2一sinx得f(x,y)=x2y+xy2+cosx+h(y),
由f(0,y)=2y+3得h(y)=2y+2,
故f(x,y)=x2y+xy2+cosx+2y+2.
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