18.下列式子中,错误的是( )
| A. | $\sqrt{2}$×$\sqrt{8}$=4 | B. | $\sqrt{(-4)×(-9)}$=$\sqrt{-4}$×$\sqrt{-9}$ | C. | $\sqrt{\frac{4}{3}}$=$\frac{2}{3}$$\sqrt{3}$ | D. | $\frac{4\sqrt{18}}{2\sqrt{6}}$=2$\sqrt{3}$ |
10.若二次函数y=-x2-3x+2的自变量x分别取x1、x2、x3,且x1、x2、x3,且0<x1<x2<x3,则对应的函数值y1、y2、y3的大小关系正确的是( )
0 283151 283159 283165 283169 283175 283177 283181 283187 283189 283195 283201 283205 283207 283211 283217 283219 283225 283229 283231 283235 283237 283241 283243 283245 283246 283247 283249 283250 283251 283253 283255 283259 283261 283265 283267 283271 283277 283279 283285 283289 283291 283295 283301 283307 283309 283315 283319 283321 283327 283331 283337 283345 366461
| A. | y3<y2<y1 | B. | y1<y2<y3 | C. | y1<y3<y2 | D. | y2<y3<y1 |