若x^4+y^4=15,x^2y=-3,求x^4-2y^4-3xy^2+x^y+2xy^2+3y^2
=x^4-2y^4-3xy^2+yx^2+2xy^2+3y^4=x^4+y^4+yx^2-xy^2=15+(-3)=12
举一反三
- 应用Matlab软件计算行列式[img=110x88]17da5d7b00219d6.png[/img]为( ). A: x^2 - 6*x^2*y^2 + 8*x*y^3 - 3*y^4 B: x^3 - 6*x^2*y^2 + 8*x*y^3 - 3*y^4 C: x^4 - 6*x^2*y^2 + 8*x*y^3 - 3*y^4 D: x^5- 6*x^2*y^2 + 8*x*y^3 - 3*y^4
- 分解因式()x()3()y()-()2()x()2()y()2()+()xy()3()正确的是A.()xy()(()x()+()y())()2()B.()xy()(()x()2()﹣()2()xy()+()y()2())()C.()xy()(()x()2()+2()xy()﹣()y()2())()D.()xy()(()x()﹣()y())()2
- 设\(z = u{e^v}\),\(u = {x^2} + {y^2}\),\(v = xy\),则\( { { \partial z} \over {\partial y}}=\)( )。 A: \({e^{xy}}({x}y^2 + {x^3} + 2y)\) B: \({e^{xy}}({x^2}y + {x^3} + 2y)\) C: \({e^{xy}}({x}y^2 + {x^3} + 2x)\) D: \({e^{xy}}({x}y+ {x^3} + 2y)\)
- 9. 已知函数$z=z(x,y)$由${{z}^{3}}-3xyz={{a}^{3}}$确定,则$\frac{{{\partial }^{2}}z}{\partial x\partial y}=$( ) A: $\frac{z({{z}^{4}}-2xy{{z}^{2}}-{{x}^{2}}{{y}^{2}})}{{{({{z}^{2}}-xy)}^{3}}}$ B: $\frac{z({{z}^{4}}-2xy{{z}^{2}}-xy)}{{{({{z}^{2}}-xy)}^{2}}}$ C: $\frac{z({{z}^{3}}-2xyz-{{x}^{2}}{{y}^{2}})}{{{({{z}^{2}}-xy)}^{3}}}$ D: $\frac{z({{z}^{3}}-2xy{{z}^{2}}-{{x}^{2}}y)}{{{({{z}^{2}}-xy)}^{3}}}$
- 已知int x=3,y=4;,写出下列表达式的值 (1) (x,y) (2) x>y?x:y (3) x?y:x (4) (x>y)?(y>=2)?1:2:(y>x)?x:y
内容
- 0
设\(z = u{e^v}\),\(u = {x^2} + {y^2}\),\(v = xy\),则\( { { \partial z} \over {\partial x}}=\) A: \({e^{xy}}({x^2}y + {y^3} + 2x)\) B: \({e^{xy}}({x}y^2 + {y^3} + 2x)\) C: \({e^{xy}}({x}y + {y^3} + 2x)\) D: \({e^{xy}}({x^2}y + {y^2} + 2x)\)
- 1
设随机变量X,Y有E(X)=3/4, E(Y)=1/2, E(XY)=1/2, 则Cov(X,Y)= ____(a/b)
- 2
设矩阵,已知A的特征值是λ1=2,λ2=λ3=1,则()。 A: x=-4,y=3 B: x=-4,y=-3 C: x=4,y=-3 D: x=4,y=3
- 3
设随机变量X,Y有E(X)=2/3,E(Y)=6, E(XY)=4 ,则Cov(X,Y) =____
- 4
已知E(X)=2,E(Y)=3,E(XY)=4,则随机变量X,Y的协方差Cov(X,Y)= 。 A: -2 B: 2 C: 6 D: 10