20.小红问老师的年龄有多大时,老师说:“我像你这么大时,你才4岁,等你像我这么大时,我就49岁了,设老师今年x岁,小红今年y岁”,根据题意可列方程为( )
| A. | $\left\{\begin{array}{l}{x-y=y+4}\\{x-y=49+x}\end{array}\right.$ | B. | $\left\{\begin{array}{l}{x-y=y+4}\\{x-y=49-x}\end{array}\right.$ | ||
| C. | $\left\{\begin{array}{l}{x-y=y-4}\\{x-y=49+x}\end{array}\right.$ | D. | $\left\{\begin{array}{l}{x-y=y-4}\\{x-y=49-x}\end{array}\right.$ |
19.下列说法中:①±3都是27的立方根,②$\root{3}{{y}^{2}}$=y,③$\sqrt{64}$的立方根是2,④$\root{3}{(±8)^{2}}$=±4.其中正确的有( )
0 293229 293237 293243 293247 293253 293255 293259 293265 293267 293273 293279 293283 293285 293289 293295 293297 293303 293307 293309 293313 293315 293319 293321 293323 293324 293325 293327 293328 293329 293331 293333 293337 293339 293343 293345 293349 293355 293357 293363 293367 293369 293373 293379 293385 293387 293393 293397 293399 293405 293409 293415 293423 366461
| A. | 1个 | B. | 2个 | C. | 3个 | D. | 4个 |