12.直角三角形两直角边分别为6cm和8cm,则斜边长为( )
| A. | 10cm | B. | 11cm | C. | 12cm | D. | 13cm |
9.
如图,己知 AB∥CD,∠BAD 和∠BCD 的平分线交于点E,∠1=100°,∠BAD=m°,则∠AEC的度数为( )
| A. | m° | B. | (40+$\frac{m}{2}$)° | C. | (40-$\frac{m}{2}$)° | D. | (50+$\frac{m}{2}$)° |
8.下列说法不一定正确的是( )
| A. | 对顶角相等 | B. | 若同位角相等,则两直线平行 | ||
| C. | 若两直线平行,则内错角相等 | D. | 同旁内角互补 |
7.
如图,将正方形ABCD的一角折叠,折痕为AE,∠B′AD比∠BAE大39°.设∠BAE和∠B′AD的度数分别为x,y,那么x,y所适合的一个方程组是( )
| A. | $\left\{\begin{array}{l}{y-x=39}\\{y+x=90}\end{array}\right.$ | B. | $\left\{\begin{array}{l}{y-x=39}\\{y+2x=90}\end{array}\right.$ | C. | $\left\{\begin{array}{l}{y-x=39}\\{y=2x}\end{array}\right.$ | D. | $\left\{\begin{array}{l}{x-y=39}\\{y+2x=90}\end{array}\right.$ |
6.满足下列条件的三条线段a、b、c能构成三角形的是( )
0 285445 285453 285459 285463 285469 285471 285475 285481 285483 285489 285495 285499 285501 285505 285511 285513 285519 285523 285525 285529 285531 285535 285537 285539 285540 285541 285543 285544 285545 285547 285549 285553 285555 285559 285561 285565 285571 285573 285579 285583 285585 285589 285595 285601 285603 285609 285613 285615 285621 285625 285631 285639 366461
| A. | a:b:c=1:2:3 | B. | a+b=4,a+b+c=9 | C. | a=3,b=4,c=5 | D. | a:b:c=1:1:2 |