19.计算3.8×10-7-3.7×10-7,结果用科学记数法表示为( )
| A. | 0.1×10-7 | B. | 1×10-6 | C. | 0.1×10-8 | D. | 1×10-8 |
18.下列方程中,属于二元一次方程的是( )
| A. | x+$\frac{1}{y}$=2 | B. | xy+5=-4 | C. | 3x2+y=8 | D. | x+$\frac{y}{4}$=2 |
17.某渔场去年计划养殖鲢鱼和鲤鱼共12t,实际养殖了14t,其中链鱼超产12%,鲤鱼超产8%,耶么该渔场去年计划养殖鲢鱼和鲤鱼各多少吨?若设该渔场去年计划养殖链鱼xt,鲤鱼yt,可列方程组为( )
| A. | $\left\{\begin{array}{l}{x+y=12}\\{12%x+8%y=14}\end{array}\right.$ | B. | $\left\{\begin{array}{l}{x+y=12}\\{(1+12%)x+(1+8%)y=14}\end{array}\right.$ | ||
| C. | $\left\{\begin{array}{l}{x+y=14}\\{12%x+8%y=12}\end{array}\right.$ | D. | $\left\{\begin{array}{l}{x+y=14}\\{(1+12%)x+(1+8%)y=12}\end{array}\right.$ |
13.下列方程是二元一次方程的是( )
0 285544 285552 285558 285562 285568 285570 285574 285580 285582 285588 285594 285598 285600 285604 285610 285612 285618 285622 285624 285628 285630 285634 285636 285638 285639 285640 285642 285643 285644 285646 285648 285652 285654 285658 285660 285664 285670 285672 285678 285682 285684 285688 285694 285700 285702 285708 285712 285714 285720 285724 285730 285738 366461
| A. | $\frac{1}{2}$x-1=3x | B. | x2-3x=1 | C. | $\frac{1}{x}$=1 | D. | x+2y=9 |