15.给出下列计算:①(m-n)(-m-n)=-m2-n2;②(-2s+t)2=4s2-4st+t2;③$\frac{x+y}{x-y}$÷(x2-y2)=(x+y)2.其中正确的是( )
| A. | ①②③ | B. | ②③ | C. | ② | D. | ③ |
14.下列分式变形正确的是( )
| A. | -$\frac{2x-3}{x}$=$\frac{-2x-3}{x}$ | B. | $\frac{2x-3}{x}$=$\frac{x-1.5}{x}$ | C. | $\frac{2x-3}{x}$=$\frac{2x}{x+3}$ | D. | $\frac{2x-3}{x}$=2-$\frac{3}{x}$ |
13.《九章算术》“方程”篇中有这样一道题“今有甲乙二人持钱不知其数,甲得乙半面钱五十,乙得甲太半(注:太半,意思为三分之二)而钱亦五十.问甲、乙持钱各几何?”若设甲、乙原各持钱x,y,则根据题意可列方程组( )
| A. | $\left\{\begin{array}{l}{x+\frac{1}{2}y=50}\\{y+\frac{2}{3}x=50}\end{array}\right.$ | B. | $\left\{\begin{array}{l}{x-\frac{1}{2}y=50}\\{y-\frac{2}{3}x=50}\end{array}\right.$ | ||
| C. | $\left\{\begin{array}{l}{x+\frac{1}{2}x=50}\\{y+\frac{2}{3}y=50}\end{array}\right.$ | D. | $\left\{\begin{array}{l}{y+\frac{1}{2}x=50}\\{x+\frac{2}{3}y=50}\end{array}\right.$ |
12.
如图,直线a,b被直线c所截,∠1=62°,∠3=80°,现逆时针转动直线a至a′位置,使a′∥b,则∠2的度数是( )
| A. | 8° | B. | 10° | C. | 18° | D. | 28° |
11.下列计算正确的是( )
| A. | a3+a3=a6 | B. | (a2)3÷a4=a2 | C. | a5•a2=a10 | D. | a7÷a4•a2=a |
10.
如图,用直尺和三角尺画图:已知点P和直线a,经过点P作直线b,使b∥a,其画法的依据是( )
| A. | 同位角相等,两直线平行 | |
| B. | 两直线平行,同位角相等 | |
| C. | 过直线外一点有且只有一条直线与已知直线平行 | |
| D. | 内错角相等,两直线平行 |
9.(-$\frac{1}{3}$)0=( )
0 296493 296501 296507 296511 296517 296519 296523 296529 296531 296537 296543 296547 296549 296553 296559 296561 296567 296571 296573 296577 296579 296583 296585 296587 296588 296589 296591 296592 296593 296595 296597 296601 296603 296607 296609 296613 296619 296621 296627 296631 296633 296637 296643 296649 296651 296657 296661 296663 296669 296673 296679 296687 366461
| A. | 1 | B. | 0 | C. | -$\frac{1}{3}$ | D. | -3 |