15.若x+$\frac{1}{x}$=3,则x2+$\frac{1}{x^2}$的值为( )
| A. | 9 | B. | 7 | C. | 11 | D. | 6 |
14.
如图,已知∠1=∠2,则下列结论一定正确的是( )
| A. | ∠3=∠4 | B. | AB∥CD | C. | AD∥BC | D. | ∠B=∠D |
12.下列各式与$\sqrt{3}$是同类二次根式的是( )
| A. | $\sqrt{9}$ | B. | $\sqrt{18}$ | C. | $\sqrt{12}$ | D. | $\sqrt{6}$ |
11.
如图所示的几何体的主视图是( )
| A. | B. | C. | D. |
10.下列运算正确的是( )
| A. | x6÷x2=x3 | B. | (-x)-2=$\frac{1}{x}$ | C. | (2x3)2=4x6 | D. | (-3a2)=3a2 |
7.三元一次方程组$\left\{\begin{array}{l}{2x-3y+2z=5}\\{x-2y+3z=-6}\\{3x-y+z=3}\end{array}\right.$ 消去未知数y后,得到的方程组可能是( )
0 298529 298537 298543 298547 298553 298555 298559 298565 298567 298573 298579 298583 298585 298589 298595 298597 298603 298607 298609 298613 298615 298619 298621 298623 298624 298625 298627 298628 298629 298631 298633 298637 298639 298643 298645 298649 298655 298657 298663 298667 298669 298673 298679 298685 298687 298693 298697 298699 298705 298709 298715 298723 366461
| A. | $\left\{\begin{array}{l}{7x+z=4}\\{5x-z=12}\end{array}\right.$ | B. | $\left\{\begin{array}{l}{7x+z=4}\\{x-5z=8}\end{array}\right.$ | ||
| C. | $\left\{\begin{array}{l}{7x-z=12}\\{x-5z=28}\\{\;}\end{array}\right.$ | D. | $\left\{\begin{array}{l}{7x-z=4}\\{x-5z=12}\end{array}\right.$ |