6.下列运算正确的是( )
| A. | (a-3)2=a2-9 | B. | a2•a4=a8 | C. | $\sqrt{9}$=±3 | D. | $\root{3}{-8}$=-2 |
5.不等式组$\left\{\begin{array}{l}{x-3<1}\\{3x+2≤4x}\end{array}\right.$的解集为( )
| A. | x≤2 | B. | x<4 | C. | 2≤x<4 | D. | x≥2 |
4.一元二次方程x2-4x+4=0的根的情况是( )
0 284262 284270 284276 284280 284286 284288 284292 284298 284300 284306 284312 284316 284318 284322 284328 284330 284336 284340 284342 284346 284348 284352 284354 284356 284357 284358 284360 284361 284362 284364 284366 284370 284372 284376 284378 284382 284388 284390 284396 284400 284402 284406 284412 284418 284420 284426 284430 284432 284438 284442 284448 284456 366461
| A. | 有两个不相等的实数根 | B. | 有两个相等的实数根 | ||
| C. | 无实数根 | D. | 无法确定 |