5.
如图,已知AB=A1B,A1B1=A1A2,A2B2=A2A3,A3B3=A3A4…,若∠A=70°,则∠An-1AnBn-1(n>2)的度数为( )
| A. | $\frac{70}{{2}^{n}}$ | B. | $\frac{70}{{2}^{n+1}}$ | C. | $\frac{70}{{2}^{n-1}}$ | D. | $\frac{70}{{2}^{n+2}}$ |
20.
如图,将一张矩形纸片ABCD折叠,使顶点C落在C′处,测量得AB=4,DE=8,则sin∠C′ED为( )
0 295485 295493 295499 295503 295509 295511 295515 295521 295523 295529 295535 295539 295541 295545 295551 295553 295559 295563 295565 295569 295571 295575 295577 295579 295580 295581 295583 295584 295585 295587 295589 295593 295595 295599 295601 295605 295611 295613 295619 295623 295625 295629 295635 295641 295643 295649 295653 295655 295661 295665 295671 295679 366461
| A. | 2 | B. | $\frac{1}{2}$ | C. | $\frac{\sqrt{2}}{2}$ | D. | $\frac{\sqrt{3}}{2}$ |