A slightly different approach....see diagram below:
the angle between the inscribed angle legs of 18 and 25 is 45 degrees
find c using cosine law
c^2 = 18^2 + 25^2 - 2 (18)(25)(cos 45) = 312.604
Now c is also the hypotenuse of the isosceles triangle formed by the two radii
use pythagorean theorem
r^2 + r^2 = c^2
2 r^2 = 312.604
r = 12.50 inches Hmmmmmm.....not the same as CPhill's answer....but close ! ~ EP
OK...I see what I did differently....I went to the points of contact at the wall.....not directly to the walls !!!
SEE CPhill's answer ......it is best !!!!!!!!!
