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初中数学七年级下册(573题)

第341题

已知等式\(y = a{x^2} + bx + c\)，当\(x = - 1\)时，\(y = 4\)；当\(x = 1\)时，\(y = 8\)；当\(x = 2\)时，\(y = 25\)；则当\(x = 3\)时，\(y = \)___。

参考答案：52

第342题

解方程组\(\left\{ {\begin{array}{*{20}{l}}
{3x - 2y + z = 3} \\
{2x + y - z = 4} \\
{4x + 3y + 2z = - 10}
\end{array}} \right.\)

参考答案：\(\left\{ {\begin{array}{*{20}{l}}
{x = 1} \\
{y = - 2} \\
{z = - 4}
\end{array}} \right.\)．

第343题

如果\(\frac{{x + 3}}{2} = \frac{{y - 1}}{3} = \frac{{z - 2}}{4}\)，且\(x + y + z = 18\)，求\(x\)，\(y\)，\(z\)的值。

参考答案：\(x = 1\)\(y = 7\)\(z = 10\)

第344题

将方程\(3x - 4y = 5\)变形为用含\(x\)的代数式表示\(y\)为\((\)　　\()\)

A.\(y = \frac{{3x - 5}}{4}\)

B.\(y = \frac{{3x + 5}}{4}\)

C.\(y = \frac{{ - 3x + 5}}{4}\)

D.\(y = \frac{{ - 3x - 5}}{4}\)

参考答案：A

第345题

参考答案：\(\left\{ {\begin{array}{*{20}{l}} {x = 13} \\ {y = 10} \end{array}} \right.\)

第346题

关于\(x\)的方程组\(\left\{ {\begin{array}{*{20}{l}} {3x - y = m} \\ {x + my = n} \end{array}} \right.\)的解是\(\left\{ {\begin{array}{*{20}{l}} {x = 1} \\ {y = 1} \end{array}} \right.\)，则\(|m - n|\)的值是___．

参考答案：1

第347题

若\({x^{m - n}} - 2{y^{m + n - 2}} = 2018\)．是关于\(x\)，\(y\)的二元一次方程，则\(m\)，\(n\)的值分别是\((\)　　\()\)

A.\(m = 1\)，\(n = 0\)

B.\(m = 0\)，\(n = 1\)

C.\(m = 2\)，\(n = 1\)

D.\(m = 2\)，\(n = 3\)

参考答案：C

第348题

在解方程组\(\left\{ {\begin{array}{*{20}{l}} {ax + 5y = 10} \\ {4x - by = - 4} \end{array}} \right.\)时，由于粗心，甲看错了方程组中的\(a\)，得到的解为\(\left\{ {\begin{array}{*{20}{l}} {x = - 3} \\ {y = - 1} \end{array}} \right.\)乙看错了方程组中的\(b\)，得到的解为\(\left\{ {\begin{array}{*{20}{l}} {x = 5} \\ {y = 4} \end{array}} \right.\)则原方程组的解___．

参考答案：\(\left\{ {\begin{array}{*{20}{l}} {x = 15} \\ {y = 8} \end{array}} \right.\)

第349题

\(\left\{ {\begin{array}{*{20}{l}}
{3x + 5y = 19①} \\
{8x - 3y = 67②}
\end{array}} \right.\)；

参考答案：\(\left\{ {\begin{array}{*{20}{l}}
{x = 8} \\
{y = - 1}
\end{array}} \right.\)

第350题

\(\left\{ {\begin{array}{*{20}{l}}
{\frac{{x - 3}}{2} - 3\left( {y - 1} \right) = 0①} \\
{2\left( {x - 3} \right) - 2\left( {y - 1} \right) = 0②}
\end{array}} \right.\)．

参考答案：\(\left\{ {\begin{array}{*{20}{l}}
{x = 3} \\
{y = 1}
\end{array}} \right.\)

第351题

\(\left\{ {\begin{array}{*{20}{l}}
{x - y = 4} \\
{2x + y = 5}
\end{array}} \right.\)；

参考答案：\(\left\{ {\begin{array}{*{20}{l}}
{x = 3} \\
{y = - 1}
\end{array}} \right.\)

第352题

\(\left\{ {\begin{array}{*{20}{l}}
{4x = - 5y - 2} \\
{2x + 3y = 2}
\end{array}} \right.\)．

参考答案：\(\left\{ {\begin{array}{*{20}{l}}
{x = - 8} \\
{y = 6}
\end{array}} \right.\)

第353题

用适当的方法解下列方程组：

\(\left\{ {\begin{array}{*{20}{l}}
{5x - 2y = 3} \\
{x + 6y = 11}
\end{array}} \right.\)；

参考答案：\(\left\{ {\begin{array}{*{20}{l}}
{x = \frac{5}{4}} \\
{y = \frac{{13}}{8}}
\end{array}} \right.\)

第354题

用适当的方法解下列方程组：

\(\left\{ {\begin{array}{*{20}{l}}
{x - y = 1} \\
{x + 3y + z = 10} \\
{x - 2y - z = - 2}
\end{array}} \right.\)．

参考答案：\(\left\{ {\begin{array}{*{20}{l}}
{x = 3} \\
{y = 2} \\
{z = 1}
\end{array}} \right.\)

第355题

已知\(\frac{a}{6} = \frac{b}{5} = \frac{c}{4} \ne 0\)，且\(a + b - 2c = 3\)，求\(a\)的值．

参考答案：6

第356题

若\(\left\{ {\begin{array}{*{20}{l}}
{x = 1} \\
{y = - 2}
\end{array}} \right.\)是方程\(3x + by = 1\)的解，则\(b\)的值为\((\)　　\()\)

A.1

B.\( - 1\)

C.\( - 2\)

D.2

参考答案：A

第357题

用加减法解方程组\(\left\{ {\begin{array}{*{20}{l}}
{5x + y = 4(1)} \\
{7x + 2y = - 9(2)}
\end{array}} \right.\)时，（1）\( \times 2 - \)（2）得\((\)　　\()\)

A.\(3x = - 1\)

B.\( - 2x = 13\)

C.\(17x = - 1\)

D.\(3x = 17\)

参考答案：D

第358题

已知方程\(3x - 4y = 5\)，用含\(x\)的式子表示\(y\)正确的是\((\)　　\()\)

A.\(x = \frac{{5 + 4y}}{3}\)

B.\(y = \frac{{5 - 3x}}{4}\)

C.\(x = \frac{{5 - 4y}}{3}\)

D.\(y = \frac{{3x - 5}}{4}\)

参考答案：D

第359题

若\((k - 2){x^{|k| - 1}} - 3y = 2\)是关于\(x\),\(y\)的二元一次方程,那么\({k^2} - 3k - 2\)的值为\((\)　　\()\)

A.8

B.8或\( - 4\)

C.\( - 8\)

D.\( - 4\)

参考答案：A

第360题

已知\(x\)、\(y\)满足方程组\(\left\{ {\begin{array}{*{20}{l}}
{x + 5y = 12} \\
{3x - y = 4}
\end{array}} \right.\)，则\(x + y\)的值为\((\)　　\()\)

A.\( - 4\)

B.4

C.\( - 2\)

D.2

参考答案：B

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