diketahui ΔABC siku siku di B dengan jari jari lingkaran dalam r. jika AB= 18 cm dan BC= 24 cm, carilah nilai r

AB² + BC² = AC²
18² + 24² = AC²
AC² = 324 + 576
AC² = 900
AC = 30 cm

r = L ∆ABC / s

s = ½ × (AB + BC + AC)
= ½ × ( 18 + 24 + 30)
= ½ × 72
= 36 cm

L ∆ABC = ½ × AB × BC
= ½ × 18 × 24
= 216 cm²

r = L ∆ABC / s
= 216 / 6
= 6 cm

jadi, nilai r = 6 cm