pilz+pnozx2.1接线图

尉泪蚁722已知三分之x=四分之y=五分之z求X^2+y^2+z^2分之xy+yz+zx -
滑红炭17397073557 ______ 答案为:47/50 可以设三分之x=四分之y=五分之z=k 则:x=3k, y=4k, z=5k.即可得到答案.

尉泪蚁722解方程组xy+xz=8 - x^2,yx+yz=12 - y^2,zy+zx= - 4 - z^2 -
滑红炭17397073557 ______ 解:xy+xz=8-x² yx+yz=12-y² zy+zx=-4-z² x(x+y+z)=8 y(x+y+z)=12 z(x+y+z)=-4 (x+y+z)²=8+12-4=16 x+y+z=±4 则①x+y+z=4时 x=4-y-z 代入yx+yz=12-y²和 zy+zx=-4-z²,则y=3 z=-1 则x=2,y=3,z=-1 ②x+y+z=-4时同理得x=-2,y=-3,z=1

尉泪蚁722已知xyz=1,x+y+z=2,x二次方+y二次方+z二次方=16,求1/(xy+2z)+1/(xz+2y)+1/(yz+2x)=? -
滑红炭17397073557 ______ xy+2z=xy+4-2x-2y=(x-2)(y-2), yz+2x=(y-2)(z-2) zx+2y=(z-2)(x-2). (x+y+z)^2=4=x^2+y^2+z^2+2(xy+yz+zx)=16+2(xy+yz+zx), xy+yz+zx=-6 (x-2)(y-2)(z-2)=xyz-2(xy+yz+zx)+4(x+y+z)-8=13

尉泪蚁722z=x/根号下x^2+y^2,求全微分 -
滑红炭17397073557 ______ zx=[√(x²+y²)-x²/√(x²+y²)]/(x²+y²)=y²/(x²+y²)^(3/2) zy=[0*√(x²+y²)-xy/√(x²+y²)]/(x²+y²)=-xy/(x²+y²)^(3/2) 所以 dz=zxdx+zydy=y²/(x²+y²)^(3/2)dx-xy/(x²+y²)^(3/2)dy

尉泪蚁722A.B.C是三角形三内角,求证:x^2+y^2+z^2>=2yzcosA+2zxcosB+2xycosC -
滑红炭17397073557 ______ 利用余弦公式:z^2=x^2+y^2-2xycosC.可以化简为2z^2>=2z(ycosA+xcosB)消掉公因子,利用三角性质显然成立.得证.

尉泪蚁722x+y分之xy=10 y+z分之yz=2 z+x分之zx=3 x=多少 -
滑红炭17397073557 ______ (x+y)/xy=10,(y+z)/yz=2,(z+x)/zx=3 1/x+1/y=10,1/y+1/z=2, 1/z+1/x=3三式相加,得2(1/x+1/y+1/z)=15,1/x+1/...

尉泪蚁722对称式的问题 -
滑红炭17397073557 ______ 1,即证f(y,x,z)=f(x,z,y)=f(z,y,x) 2,f(x,y,z)=x(y-z)^2+y(z-x)^2+z(x-y)^2 =xy^2-2xyz+xz^2+yz^2-2xyz+yx^2+zx^2-2xyz+zy^2 =(x+y+z)(xy+yz+zx)-3xyz-6xyz =(x+y+z)(xy+yz+zx)-9xyz

尉泪蚁722设x,y,z为正实数.求证 -
滑红炭17397073557 ______ 设x,y,z为正实数.求证 x^2/(x^2+y^2+xy)+y^2/(y^2+z^2+yz)+z^2/(z^2+x^2+zx)>=1 证明 去分母得: x^2*(y^2+z^2+yz)*(z^2+x^2+zx)+y^2*(z^2+x^2+zx)*(x^2+y^2+xy)+z^2*(x^2+y^2+xy)(y^2+z^2+yz)>=(y^2+z^2+yz)*(z^2+x^2+zx)*(x^2+y^2+xy) 展开...

尉泪蚁722苹果+梨子=250g 苹果+桃子=180g 梨子+桃子=230g 三种水果各种多少克 -
滑红炭17397073557 ______ 设苹果X梨子Y桃子ZX+Y=250X+Z=180Y+Z=230解得X=100 Y=150 Z=80

尉泪蚁722怎么把xy+(yz+zx)2化简 -
滑红炭17397073557 ______[答案] 无法化简,