Tolong bantu no.31 + caranya

r = L/s

s = (AB + AC + BC )/2
s = (21 + 24 + 24 )/2
s = 69/2
s = 34,5 cm

L = √s(s-AB)(s-BC)(s-AC)
L = √34,5(34,5-21)(34,5-24)(34,5-24)
L = √34,5(13,5)(10,5)(10,5)
L = √ 51348,9375
L = 226,603039 cm²

r = L/s
r = 226,603039/34,5
r = 6,56 cm