13.
如图,∠AOB=45°,点C在OB上,OC=8,若以点C为圆心、r为半径的圆与OA相切,则r等于( )
| A. | 4 | B. | 4$\sqrt{2}$ | C. | 4$\sqrt{3}$ | D. | 8 |
9.已知A32=3×2=6,A52=5×4=20,A63=6×5×4=120,依此规律A74=( )
| A. | 480 | B. | 360 | C. | 840 | D. | 1080 |
7.观察下列各图中小圆点的摆放规律,按这样的规律继续摆放下去,则第⑦个图形中小圆点的个数为( )

0 288482 288490 288496 288500 288506 288508 288512 288518 288520 288526 288532 288536 288538 288542 288548 288550 288556 288560 288562 288566 288568 288572 288574 288576 288577 288578 288580 288581 288582 288584 288586 288590 288592 288596 288598 288602 288608 288610 288616 288620 288622 288626 288632 288638 288640 288646 288650 288652 288658 288662 288668 288676 366461
| A. | 62 | B. | 64 | C. | 66 | D. | 68 |