10.设x,y满足约束条件$\left\{\begin{array}{l}{x≤3}\\{x+y≥0}\\{x-y+6≥0}\end{array}\right.$,若z=ax+y的最大值为3a+9,最小值为3a-3,则a的取值范围是( )
| A. | a≤-1 | B. | a≥1 | C. | -1≤a≤1 | D. | a≥1或a≤-1 |
9.已知双曲线$\frac{{x}^{2}}{{a}^{2}}$-$\frac{{y}^{2}}{{b}^{2}}$=1的离心率为$\frac{\sqrt{5}}{2}$,过右焦点的直线与两条渐近线分别交于A,B,且与其中一条渐近线垂直,若△OAB的面积为$\frac{16}{3}$,其中O为坐标原点,则双曲线的焦距为( )
0 227420 227428 227434 227438 227444 227446 227450 227456 227458 227464 227470 227474 227476 227480 227486 227488 227494 227498 227500 227504 227506 227510 227512 227514 227515 227516 227518 227519 227520 227522 227524 227528 227530 227534 227536 227540 227546 227548 227554 227558 227560 227564 227570 227576 227578 227584 227588 227590 227596 227600 227606 227614 266669
| A. | 2$\sqrt{3}$ | B. | 2$\sqrt{5}$ | C. | 2$\sqrt{10}$ | D. | 2$\sqrt{15}$ |