4.若x>0,y>0,x+y=1,则$\frac{x^2}{x+2}+\frac{y^2}{y+1}$的最小值为( )
| A. | $\frac{1}{4}$ | B. | $\frac{{\sqrt{3}}}{2}$ | C. | $\frac{{\sqrt{2}}}{4}$ | D. | $\frac{1}{2}$ |
3.已知函数f(x)满足f($\frac{1}{x}$)+$\frac{1}{x}$f(-x)=2x(x≠0),则f(-2)=( )
| A. | $-\frac{7}{2}$ | B. | $\frac{9}{2}$ | C. | $\frac{7}{2}$ | D. | $-\frac{9}{2}$ |
2.已知双曲线C1:x2-y2=a2(a>0)关于直线y=x-2对称的曲线为C2,若直线2x+3y=6与C2相切,则实数a的值为( )
| A. | $\frac{{2\sqrt{5}}}{5}$ | B. | $\frac{8}{5}$ | C. | $\frac{4}{5}$ | D. | $\frac{{8\sqrt{5}}}{5}$ |
1.若同时掷两枚骰子,则向上的点数和是6的概率为( )
| A. | $\frac{1}{6}$ | B. | $\frac{1}{12}$ | C. | $\frac{5}{36}$ | D. | $\frac{5}{18}$ |
20.已知实数x,y满足约束条件$\left\{\begin{array}{l}x-y≥0\\ x+2y≤4\\ x-2y≤2\end{array}\right.$,则目标函数z=x+3y的最大值为( )
0 238393 238401 238407 238411 238417 238419 238423 238429 238431 238437 238443 238447 238449 238453 238459 238461 238467 238471 238473 238477 238479 238483 238485 238487 238488 238489 238491 238492 238493 238495 238497 238501 238503 238507 238509 238513 238519 238521 238527 238531 238533 238537 238543 238549 238551 238557 238561 238563 238569 238573 238579 238587 266669
| A. | $\frac{16}{3}$ | B. | $\frac{9}{2}$ | C. | -8 | D. | $\frac{17}{2}$ |