∴a2+(−
2 |
n |
2 |
n |
解得a=
4n+4 |
2n+1 |
∴O为(
4n+4 |
2n+1 |
∴圆O的半径为OA=4+
2 |
n |
4n+4 |
2n+1 |
4n2+4n+2 |
n(2n+1) |
∴其外接圆的面积Sn=π• [
4n2+4n+2 |
2n2+n |
4+
| ||||
2+
|
∴
lim |
n→∞ |
故答案是4π.
2 |
n |
2 |
n |
2 |
n |
lim |
n→∞ |
2 |
n |
2 |
n |
4n+4 |
2n+1 |
4n+4 |
2n+1 |
2 |
n |
4n+4 |
2n+1 |
4n2+4n+2 |
n(2n+1) |
4n2+4n+2 |
2n2+n |
4+
| ||||
2+
|
lim |
n→∞ |