Perhatikan gambar di samping. Jika keliling segitiga ABC adalah 88 cm, panjang AC adalah ... cm.

AB = m + 4
BC = AC = 2m - 8
∆ ABC sama kaki
Keliling = 88 cm
88 = 2( 2m - 8) + ( m + 4)
88 = 4m - 16 + m + 4
88 = 5m - 12
5m = 100
m = 100/5 = 20
AB = 20 + 4 = 24 cm
AC = BC = 2( 20) - 8 = 40-8 = 32 cm