13.下列等式正确的是( )
| A. | $\sqrt{\frac{9}{16}}$=±$\frac{3}{4}$ | B. | $\root{3}{-9}=-3$ | C. | $\sqrt{(-\frac{1}{3})^{2}}=\frac{1}{3}$ | D. | $\sqrt{-1\frac{7}{9}}=1\frac{1}{3}$ |
10.下列各组数是方程组$\left\{\begin{array}{l}{x+y=5}\\{2x-y=1}\end{array}\right.$的解的是( )
| A. | $\left\{\begin{array}{l}{x=2}\\{y=3}\end{array}\right.$ | B. | $\left\{\begin{array}{l}{x=1}\\{y=4}\end{array}\right.$ | C. | $\left\{\begin{array}{l}{x=3}\\{y=2}\end{array}\right.$ | D. | $\left\{\begin{array}{l}{x=4}\\{y=1}\end{array}\right.$ |
9.下列计算正确的是( )
0 283387 283395 283401 283405 283411 283413 283417 283423 283425 283431 283437 283441 283443 283447 283453 283455 283461 283465 283467 283471 283473 283477 283479 283481 283482 283483 283485 283486 283487 283489 283491 283495 283497 283501 283503 283507 283513 283515 283521 283525 283527 283531 283537 283543 283545 283551 283555 283557 283563 283567 283573 283581 366461
| A. | (x4)4=x8 | B. | (mn)2(-m4)=-m6n2 | C. | a2•a3=a6 | D. | 2x(-3xy)2=-6x3y2 |