如果函数z=f(x,y)满足,且f(x,1)=x+2,f’y(x,1)=x+1,则f(x,y)=______.

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问题 如果函数z=f(x,y)满足,且f(x,1)=x+2,f’y(x,1)=x+1,则f(x,y)=______.

选项

答案y2+xy-y+2

解析两边对y积分,得
    f’y(x,y)=2y+φ1(x),
将f’y(x,1)=x+1代入上式,得φ1(x)=x-1,于是
    f’y(x,y)=2y+x-1,
将上式两边对y积分,得
    f(x,y)=y2+xy-y+φ2(x),
将f(x,1)=x+2代入上式,得φ2(x)=2,故
    f(x,y)=y2+xy-y+2.
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