18.
如图,正比例函数y1=kx和反比例函数y2=$\frac{2}{x}$的图象交于A(-1,2)、(1,-2)两点,若y1<y2,则x的取值范围是( )
| A. | x<-1或x>1 | B. | x<-1或0<x<1 | C. | -1<x<0或 0<x<1 | D. | -1<x<0或x>1 |
13.下列计算正确的是( )
| A. | (x+7)(x-8)=x2+x-56 | B. | (x+2)2=x2+4 | ||
| C. | (7-2x)(8+x)=56-2x2 | D. | (3x+4y)(3x-4y)=9x2-16y2 |
12.若25x2+30xy+k是一个完全平方式,则k是( )
| A. | 36y2 | B. | 9y2 | C. | 6y2 | D. | y2 |
11.若x2-y2=20,且x+y=-5,则x-y的值是( )
0 309420 309428 309434 309438 309444 309446 309450 309456 309458 309464 309470 309474 309476 309480 309486 309488 309494 309498 309500 309504 309506 309510 309512 309514 309515 309516 309518 309519 309520 309522 309524 309528 309530 309534 309536 309540 309546 309548 309554 309558 309560 309564 309570 309576 309578 309584 309588 309590 309596 309600 309606 309614 366461
| A. | 5 | B. | 4 | C. | -4 | D. | 以上都不对 |