19.在下列性质中,矩形具有而菱形不一定有的是( )
| A. | 四个角是直角 | B. | 四条边相等 | C. | 对角线互相垂直 | D. | 对角线互相平分 |
18.
如图.已知△ABC的内切圆半径为1,外接圆半径为$\frac{5}{2}$,I是△ABC的内心,AI的延长线交△ABC的外接圆于点P,则IA•IP的值为( )
| A. | $\frac{5}{2}$ | B. | $\frac{25}{4}$ | C. | 5 | D. | $\frac{25}{2}$ |
17.若方程组$\left\{\begin{array}{l}{x+y=3m①}\\{x-y=7m②}\end{array}\right.$的解也是二元一次方程3x+5y=10的解,则m的值应为( )
0 284272 284280 284286 284290 284296 284298 284302 284308 284310 284316 284322 284326 284328 284332 284338 284340 284346 284350 284352 284356 284358 284362 284364 284366 284367 284368 284370 284371 284372 284374 284376 284380 284382 284386 284388 284392 284398 284400 284406 284410 284412 284416 284422 284428 284430 284436 284440 284442 284448 284452 284458 284466 366461
| A. | -2 | B. | 1 | C. | $\frac{1}{2}$ | D. | 2 |