20.关于x的二次三项式4x2-kx+9是一个完全平方式,则k的值为( )
| A. | -12 | B. | ±12 | C. | ±6 | D. | 6 |
19.下列计算中,错误的是( )
| A. | (b-a)3÷(a-b)2=b-a | B. | (a-b)5÷(a-b)3=÷(a-b)2 | C. | (a+b)3÷(-a-b)2=a+b | D. | (x-2)5÷(2-x)3=(x-2)2 |
15.下列各式的计算结果中,不正确的是( )
| A. | x+4x=5x | B. | 3ab-2ab=ab | C. | -5x2y+7xy2=2x2y | D. | 4m+2n-(n-m)=5m+n |
14.已知-2x2ym与4x1-ny4是同类项,则mn的值为( )
0 293304 293312 293318 293322 293328 293330 293334 293340 293342 293348 293354 293358 293360 293364 293370 293372 293378 293382 293384 293388 293390 293394 293396 293398 293399 293400 293402 293403 293404 293406 293408 293412 293414 293418 293420 293424 293430 293432 293438 293442 293444 293448 293454 293460 293462 293468 293472 293474 293480 293484 293490 293498 366461
| A. | 4 | B. | -4 | C. | 8 | D. | -8 |