Answer:

Given,

∆ ABC is an isosceles triangle.

AB = AC = 13 cm

The altitude from A on BC meets BC at D.

D is the midpoint of BC.

AD = 5 cm

∆ ???????????? ???????????? ∆ ???????????? are right-angled triangles.

Applying Pythagoras theorem,

????????² = ????????² + ????????²

????????² = ????????² − ????????²

=>13² − 5²

=>169 − 25

=>144

=>√144

=>12

BC = 2(BD)

=>2 × 12

=>24 cm.