7.在-1.732,$\sqrt{2}$,π,3.$\stackrel{••}{14}$,2+$\sqrt{3}$,3.212212221…,6.5这些数中,无理数的个数为( )
| A. | 5 | B. | 2 | C. | 3 | D. | 4 |
6.根据下表回答下列问题:
(1)795.24的算术平方根是28.4;
(2)$\sqrt{823.7}$≈28.7;
(3)$\sqrt{810}$在哪两个数之间?答:在28.4与28.5.
0 282198 282206 282212 282216 282222 282224 282228 282234 282236 282242 282248 282252 282254 282258 282264 282266 282272 282276 282278 282282 282284 282288 282290 282292 282293 282294 282296 282297 282298 282300 282302 282306 282308 282312 282314 282318 282324 282326 282332 282336 282338 282342 282348 282354 282356 282362 282366 282368 282374 282378 282384 282392 366461
| x | 28.0 | 28.1 | 28.2 | 28.3 | 28.4 | 28.5 | 28.6 | 28.7 | 28.8 |
| x2 | 784.00 | 789.61 | 795.24 | 800.89 | 806.56 | 812.25 | 817.96 | 823.69 | 829.44 |
(2)$\sqrt{823.7}$≈28.7;
(3)$\sqrt{810}$在哪两个数之间?答:在28.4与28.5.