5.
我国古代《易经》一书中记载,远古时期,人们通过在绳子上打结来记录数量,即“结绳计数”.如图,一位母亲在从右到左依次排列的绳子上打结,满七进一,用来记录孩子自出生后的天数,由图可知,孩子自出生后的天数是( )
| A. | 84 | B. | 336 | C. | 510 | D. | 1326 |
4.
如图,在Rt△ABC中,∠B=90°,∠A=30°,以点A为圆心,BC长为半径画弧交AB于点D,分别以点A、D为圆心,AB长为半径画弧,两弧交于点E,连接AE,DE,则∠EAD的余弦值是( )
0 284439 284447 284453 284457 284463 284465 284469 284475 284477 284483 284489 284493 284495 284499 284505 284507 284513 284517 284519 284523 284525 284529 284531 284533 284534 284535 284537 284538 284539 284541 284543 284547 284549 284553 284555 284559 284565 284567 284573 284577 284579 284583 284589 284595 284597 284603 284607 284609 284615 284619 284625 284633 366461
| A. | $\frac{\sqrt{3}}{12}$ | B. | $\frac{\sqrt{3}}{6}$ | C. | $\frac{\sqrt{3}}{3}$ | D. | $\frac{\sqrt{3}}{2}$ |