20.
如图,在矩形ABCD中,E是AD边的中点,BE⊥AC,垂足为点F,连接DF,分析下列四个结论:①△AEF∽△CAB;②CF=2AF;③DF=DC;④S△ABC=2S△ABF.其中正确的结论有( )
| A. | 4个 | B. | 3个 | C. | 2个 | D. | 1个 |
19.
如图,一条公路的转弯处是一段圆弧(图中的$\widehat{AB}$),点O是这段弧的圆心,C是$\widehat{AB}$上一点,OC⊥AB,垂足为D,AB=160m,CD=40m,则这段弯路的半径是( )
| A. | 60m | B. | 80m | C. | 100m | D. | 120m |
18.计算[(-x)2]5=( )
| A. | x7 | B. | -x7 | C. | x10 | D. | -x10 |
15.已知不等式组$\left\{\begin{array}{l}x>-a\\ x≥-b\end{array}$的解为x≥-b,则下列各式正确的是( )
| A. | a>b | B. | a<b | C. | b≤a | D. | a≤b |
14.一元一次不等式2(x+1)≥4的解集在数轴上表示为( )
| A. | B. | C. | D. |
13.用尺规作图作一个角等于已知角的示意图如图所示,则说明∠A′OB′=∠AOB依据是( )

0 293233 293241 293247 293251 293257 293259 293263 293269 293271 293277 293283 293287 293289 293293 293299 293301 293307 293311 293313 293317 293319 293323 293325 293327 293328 293329 293331 293332 293333 293335 293337 293341 293343 293347 293349 293353 293359 293361 293367 293371 293373 293377 293383 293389 293391 293397 293401 293403 293409 293413 293419 293427 366461
| A. | SAS | B. | ASA | C. | SSS | D. | AAS |