1. 下列是三元一次方程组的是 ()
A. $\begin{cases}2x = 5,\\x^{2}+y = 7,\\x + y + z = 6\end{cases}$
B. $\begin{cases}\dfrac{3}{x}-y + z = -2,\\x - 2y + z = 9,\\y = -3\end{cases}$
C. $\begin{cases}x + y - z = 7,\\xyz = 1,\\x - 3y = 4\end{cases}$
D. $\begin{cases}x + y = 2,\\y + z = 1,\\x + z = 9\end{cases}$

D

2. 解方程组$\begin{cases}2x - y + 3z = 3,\\-4x + y + 2z = 11,\\5x + y + 7z = 1,\end{cases}$若要使运算简便,消元应选 ()
A. 先消$x$
B. 先消$y$
C. 先消$z$
D. 先消常数项

B

3. 三元一次方程组$\begin{cases}x - y = 6,\\x + z = 4,\\2x - y + z = 10\end{cases}$的解的个数为 ()
A. 无数多个
B. 1
C. 2
D. 0

A

4. 解方程组$\begin{cases}4x + 3z = 9,\\2x - 6y + 4z = 5,\\3x + 2y + z = 8\end{cases}$较简便的方法是 ()
A. 先消$z$,再解$\begin{cases}2x - 6y = -15,\\19x + 9y = 8\end{cases}$
B. 先消$z$,再解$\begin{cases}11x + 3y = 9,\\10x + 14y = 27\end{cases}$
C. 先消$y$,再解$\begin{cases}4x + 3z = 9,\\11x + 7z = 29\end{cases}$
D. 先消$x$,再解$\begin{cases}22y + 2z = 61,\\66y - 38z = -33\end{cases}$

C

5. 已知$x$,$y$同时满足下列三个等式:$4x + y = a + 1$,$5x + 2y = a$,$3x - 2y = 7a$,则$a$的值为 ()
A. $-2$
B. $-1$
C. 1
D. 2

C