计算：2x2•3xy=______．

2022-06-09

答案：

2x2•3xy=2×3x2•x•y=6x3y．

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: ${e^{xy}}({x}y+ {x^3} + 2y)$
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: ${e^{xy}}({x^2}y + {y^2} + 2x)$
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: $\frac{z({{z}^{3}}-2xy{{z}^{2}}-{{x}^{2}}y)}{{{({{z}^{2}}-xy)}^{3}}}$
方程$ xy'' - 5y' + 3xy = {\cos ^2}x $的通解中包含 (写数字)个独立的任意常量。______

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