20.以下面每组中的三条线段为边的三角形中,是直角三角形的是( )
| A. | 1 3 4 | B. | 1.5 2 2.5 | C. | 4 5 6 | D. | 7 8 9 |
19.一个长方体的体积是$\sqrt{48}$cm3,长是$\sqrt{6}$cm,宽是$\sqrt{2}$cm,则高是( )
| A. | 4cm | B. | 12$\sqrt{3}$cm | C. | 2cm | D. | 2$\sqrt{3}$cm |
12.下列命题中,属于真命题的是( )
0 294113 294121 294127 294131 294137 294139 294143 294149 294151 294157 294163 294167 294169 294173 294179 294181 294187 294191 294193 294197 294199 294203 294205 294207 294208 294209 294211 294212 294213 294215 294217 294221 294223 294227 294229 294233 294239 294241 294247 294251 294253 294257 294263 294269 294271 294277 294281 294283 294289 294293 294299 294307 366461
| A. | 如果a=-2,那么a2=4 | |
| B. | 如果|a|=a,那么a>0 | |
| C. | 如果两个角相等,那么这两个角都为80° | |
| D. | 如果ab=0,那么a=0 |