8.
如图正方体ABCD-A1B1C1D1,M,N分别为A1D1和AA1的中点,则下列说法中正确的个数为( )
①C1M∥AC;
②BD1⊥AC;
③BC1与AC的所成角为60°;
④B1A1、C1M、BN三条直线交于一点.
①C1M∥AC;
②BD1⊥AC;
③BC1与AC的所成角为60°;
④B1A1、C1M、BN三条直线交于一点.
| A. | 1 | B. | 2 | C. | 3 | D. | 4 |
7.已知函数f(x)=$\left\{\begin{array}{l}{{a}^{x},x>1}\\{(6-a)x,x≤1}\end{array}\right.$,若对于任意的两个不相等实数x1,x2都有$\frac{f({x}_{1})-f({x}_{2})}{{x}_{1}-{x}_{2}}$>0,则实数a的取值范围是( )
| A. | (1,6) | B. | (1,+∞) | C. | (3,6) | D. | [3,6) |
6.一梯形的直观图是如图是欧式的等腰梯形,且直观图OA′B′C′的面积为2,则原梯形的面积为( )
| A. | 2 | B. | 2$\sqrt{2}$ | C. | 4 | D. | 4$\sqrt{2}$ |
20.已知函数$f(x)=\left\{\begin{array}{l}x\\{x^2}\end{array}\right.\;\;\;\begin{array}{l}{({x≤a})}\\{({x>a})}\end{array}$,若存在实数b,使函数g(x)=f(x)-b有两个零点,则a的取值范围是( )
0 235482 235490 235496 235500 235506 235508 235512 235518 235520 235526 235532 235536 235538 235542 235548 235550 235556 235560 235562 235566 235568 235572 235574 235576 235577 235578 235580 235581 235582 235584 235586 235590 235592 235596 235598 235602 235608 235610 235616 235620 235622 235626 235632 235638 235640 235646 235650 235652 235658 235662 235668 235676 266669
| A. | a<0 | B. | a>0且a≠1 | C. | a<1 | D. | a<1且a≠0 |