15.
如图,正方形ABCD中,AB=2,E为BC中点,两个动点M和N分别在边CD和AD上运动且MN=1,若△ABE与以D、M、N为顶点的三角形相似,则DM为( )
| A. | $\frac{1}{3}$ | B. | $\frac{\sqrt{5}}{5}$ | C. | $\frac{1}{3}$或$\frac{2}{3}$ | D. | $\frac{\sqrt{5}}{5}$或$\frac{2\sqrt{5}}{5}$ |
14.关于x的一元二次方程(m2-1)x2-2(m+1)x+1=0有实数根,则m的取值范围是( )
0 294279 294287 294293 294297 294303 294305 294309 294315 294317 294323 294329 294333 294335 294339 294345 294347 294353 294357 294359 294363 294365 294369 294371 294373 294374 294375 294377 294378 294379 294381 294383 294387 294389 294393 294395 294399 294405 294407 294413 294417 294419 294423 294429 294435 294437 294443 294447 294449 294455 294459 294465 294473 366461
| A. | m>1 | B. | m≥1 | C. | m≥-1且m≠1 | D. | m>-1且m≠1 |