As the picture shows, there is a circular fountain in the center of Harmony Square. In order to measure the radius of the fountain, the math activity team selected three white marble pillars A, B and C on the pool fence, and measured AB = AC, the length of BC was 14m, and the distance from A to BC was 1m, and calculated the radius of the fountain.

Let the radius be r.

7? +(R- 1)？ =R？

49+R？ -2R+ 1-R？ =0

The solution is R=45.