fxy+x+y+怎么求
姬亭类5138求函数f(x,y)=x^3+y^3 - 9xy+ 27的极值 -
阎码邦13769202165 ______ ^fx(x,y)=3x^2-9y fy(x,y)=3y^2-9x 当fx(x,y)=0,fy(x,y)=0时 解得:x=0,y=0;或x=3,y=3 fxx(x,y)=A=6x fxy(x,y)=B=-9 fyy(x,y)=C=6y 当x=0,y=0时,AC-B^2<0,所以不是极值点 当x=3,y=3时,A=18>0,AC-B^2>0 所以为极小值点,代入有:f(3,3)=0 所以函数...
姬亭类5138f(x+y,xy)=x^2+y^2求fxy(1, -
阎码邦13769202165 ______[答案] 因为f(x+y,xy)=x^2+y^2=(x+y)^2-2xy 所以f(x,y)=x^2-2y 现对x求导得到: fx(x,y)=2x 再对y求导得到: fxy(x,y)=0. 所以无论x,y为何值,fxy(x,y)=0.即fxy(1,1)=0.
姬亭类5138求f(x,y)=(x+y^2+2y)*e^2x的极值点和最值点. -
阎码邦13769202165 ______ ^^^解; 先求偏导数:f(x,y)=(x+y^2+2y)e^(2x) fx(x,y)=e^(2x)+2(x+y^2+2y)e^(2x) fy(x,y)=(2y+2)e^(2x) 令fx(x,y)=0,fy(x,y)=01+2(x+y^2+2y)=02y+2=0 y=-1 x=1/2 fxx(x,y)=[e^(2x)(1+2x+2y^2+4y)]x=2e^(2x)+2(1+2x+2y^2+4y)e^(2x)|(x=1/2,y=-1)=2e>0 fxy(x,y)=[...
姬亭类5138题目:函数z=f(x,y)由方程xy+yz+zx=1所确定,求fxy＂ .谢谢了,大神帮忙啊 -
阎码邦13769202165 ______ z对x的偏导 xy+yz+zx=1 y+yfx'+z+xfx'=0 <1> z对y的偏导 x+z+yfy'+xfy' =0 <2> <1>z对y的偏导 1+fx'+yfxy＂+fy'+xfxy＂ =0 1+(fx'+fy')+(x+y)fxy＂=0 <3> 由<1> <2>得: 1+fx'+fy' =1-(y+z)/(x+y)-(x+z)/(x+y) =-2z/(x+y) (x+y)fxy＂=2z/(x+y) fxy＂ =2z/(x+y)^2
姬亭类5138求下列的极值 f(x.y)=x的平方+xy+y的平方 - 3x - 6y+1= -
阎码邦13769202165 ______ fx=2x+y-3=0 fy=x+2y-6=0 驻点(0,3) A=fxx=2,B=fxy=1,C=fyy=2 AC-B²=2*2-1²>0 A>0 所以 有极小值f(0,3)=9-18+1=-8
姬亭类5138偏导数fxx fxy类题目怎么解 求解题过程 -
阎码邦13769202165 ______ ∂f/∂x=fx=-4cos(2x+y)+sin(x-y) ∂f/∂y=fy=-2cos(2x+y)-sin(x-y) ∂²f/∂x²=fxx=8sin(2x+y)+cos(x-y) ∂²f/∂y²=fyy=2sin(2x+y)+cos(x-y) ∂²f/∂x∂y=fxy(原题这里写错!)=4sin(2x+y)-cos(x-y) ∂²f/∂y∂x=fyx(原题这里写错!)=4sin(2x+y)-cos(x-y)
姬亭类5138已知f(xy,x+y)=x2+y2+xy求f(x,y)
阎码邦13769202165 ______ xy=a,x+y=b f(xy,x+y)=f(a,b)= x2+y2+xy=(x+y)^2-xy=b^2-a f(x,y)=y^2-x
姬亭类5138已知f(x,y)=xy/x2+y.试求f(xy,x/y) -
阎码邦13769202165 ______ f(x,y)=xy/x2+y f(xy,x/y)=(xy*x/y)/(x²y²+x/y)=x²/(x²y²+x/y)=x/(xy²+1/y)=xy/(xy³+1)
姬亭类5138求二元函数f(x,y)=x^2+y^3+4x - 3y+4的极值,并说明是极大值还是极小值.亲,急急急 -
阎码邦13769202165 ______ f(x,y)=x^2+y^3+4x-3y+4 由f'x(x,y)=2x+4=0 f'y(x,y)=3y^2-3=0 x=-2 y=1,-1 f''xx(x,y)=2 f''xy(x,y)=0 f''yy(x,y)=6y AC-B^2=12y>0有极值 f(-2,1)极小值
姬亭类5138fxy(x,y)如何求偏导 -
阎码邦13769202165 ______[答案] 先对x求偏导把y当常数x当未知数求导得结果M再对M求偏导把x当常数y当未知数求导得结果N最后求偏导的结果就是N