20.
如图,△ABC中,∠ACB=90°,AC>BC,分别以△ABC的边AB、BC、CA为一边向△ABC外作正方形ABDE、BCMN、CAFG,连接EF、GM、ND,设△AEF、△BND、△CGM的面积分别为S1、S2、S3,则下列结论正确的是( )
| A. | S1=S2=S3 | B. | S1=S2<S3 | C. | S1=S3<S2 | D. | S2=S3<S1 |
16.
如右图所示的工件的主视图是( )
| A. | B. | C. | D. |
15.明明家离学校1500米,其中有一段为上坡路.另一段为下坡路,某天他去学校共用了12分钟,假设明明上坡路的平均速度是5千米/时,下坡路的平均速度是8千米/时.若设明明上坡路用了x分钟,下坡路用了y分钟,根据题意可列方程组为( )
0 294392 294400 294406 294410 294416 294418 294422 294428 294430 294436 294442 294446 294448 294452 294458 294460 294466 294470 294472 294476 294478 294482 294484 294486 294487 294488 294490 294491 294492 294494 294496 294500 294502 294506 294508 294512 294518 294520 294526 294530 294532 294536 294542 294548 294550 294556 294560 294562 294568 294572 294578 294586 366461
| A. | $\left\{\begin{array}{l}{x+y=12}\\{5x+8y=1500}\end{array}\right.$ | B. | $\left\{\begin{array}{l}{x+y=12}\\{\frac{1}{12}x+\frac{2}{15}y=1.5}\end{array}\right.$ | ||
| C. | $\left\{\begin{array}{l}{5x+8y=1.5}\\{x+y=12}\end{array}\right.$ | D. | $\left\{\begin{array}{l}{x+y=12}\\{\frac{1}{12}x-\frac{2}{15}y=1.5}\end{array}\right.$ |