Pada segitiga samakaki ABC panjang AB = AC = 20cm, BC = 24cm. Panjang jari-jari lingkaran dalam adalah...

t = √20² - 12²
t = √400 - 144
t = √256
t = 16

L = a x t / 2
L = 24 x 16 / 2
L = 12 x 16
L = 192cm²

S = 1/2 K
S = 1/2 (20 + 20 + 24)
S = 1/2 (64)
S = 32

r = L / S
r = 192 / 32
r = 6cm