15.下列计算正确的是( )
| A. | 3a+4b=7ab | B. | 7a-3a=4 | C. | 3ab-2ab=ab | D. | 3a+2a=5a2 |
8.四个数-5,-0.1,$\frac{1}{2}$,$\sqrt{2}$中为无理数的是( )
| A. | -5 | B. | -0.1 | C. | $\frac{1}{2}$ | D. | $\sqrt{2}$ |
7.把分式$\frac{2a}{a+b}$中的a、b都扩大5倍,则分式的值( )
0 279341 279349 279355 279359 279365 279367 279371 279377 279379 279385 279391 279395 279397 279401 279407 279409 279415 279419 279421 279425 279427 279431 279433 279435 279436 279437 279439 279440 279441 279443 279445 279449 279451 279455 279457 279461 279467 279469 279475 279479 279481 279485 279491 279497 279499 279505 279509 279511 279517 279521 279527 279535 366461
| A. | 扩大10倍 | B. | 不变 | C. | 扩大5倍 | D. | 缩小5倍 |