7.在四边形ABCD中,AD∥BC,∠B=∠C,要使四边形ABCD为矩形,还需添加一个条件,这个条件可以是( )
| A. | AB=CD | B. | AC=BD | C. | ∠A=∠D | D. | ∠A=∠B |
5.下列方程组中,是二元一次方程组的为( )
| A. | $\left\{\begin{array}{l}{x+y=1}\\{x-z=2}\end{array}\right.$ | B. | $\left\{\begin{array}{l}{{y}^{2}-1=0}\\{x-2y=0}\end{array}\right.$ | C. | $\left\{\begin{array}{l}{y-2x=1}\\{y=5}\end{array}\right.$ | D. | $\left\{\begin{array}{l}{\frac{1}{x}+3y=0}\\{x-y=1}\end{array}\right.$ |
2.在?ABCD中,∠A:∠B:∠C:∠D的值可以是( )
| A. | 1:2:3:4 | B. | 1:3:3:1 | C. | 3:3:1:1 | D. | 3:1:3:1 |
19.
如图,在?ABCD中,下列结论一定正确的是( )
0 282434 282442 282448 282452 282458 282460 282464 282470 282472 282478 282484 282488 282490 282494 282500 282502 282508 282512 282514 282518 282520 282524 282526 282528 282529 282530 282532 282533 282534 282536 282538 282542 282544 282548 282550 282554 282560 282562 282568 282572 282574 282578 282584 282590 282592 282598 282602 282604 282610 282614 282620 282628 366461
| A. | AC⊥BD | B. | AC=BD | C. | AB=AD | D. | AO=CO |