Find the area
S = the semi-perimeter = [ 17 + 17 + 18 ] / 2 = 26
Area = sqrt [ 26 (26 - 17)^2 (26 - 18) ] = 36sqrt (13)
Area = (1/2) ( perimeter) * inradius
36sqr (13) = (1/2) (52) * inradius
36 sqrt (13) = 26 * inradius
(36/26) sqrt (13) = inradius = (18 sqrt (13) ) / 13 ≈ 4.99