7.既是方程x-y=1,又是方程2x+y=5的解是( )
| A. | $\left\{\begin{array}{l}{x=-1}\\{y=2}\end{array}\right.$ | B. | $\left\{\begin{array}{l}{x=2}\\{y=-1}\end{array}\right.$ | C. | $\left\{\begin{array}{l}{x=1}\\{y=2}\end{array}\right.$ | D. | $\left\{\begin{array}{l}{x=2}\\{y=1}\end{array}\right.$ |
3.与-3x2y的乘积是9x6y3的单项式是( )
0 284554 284562 284568 284572 284578 284580 284584 284590 284592 284598 284604 284608 284610 284614 284620 284622 284628 284632 284634 284638 284640 284644 284646 284648 284649 284650 284652 284653 284654 284656 284658 284662 284664 284668 284670 284674 284680 284682 284688 284692 284694 284698 284704 284710 284712 284718 284722 284724 284730 284734 284740 284748 366461
| A. | -3x4y2 | B. | -3x3y3 | C. | -27x8y4 | D. | 12x3y3 |