Tolong yang no 3 ya

15cm..................

diket:
p = 20
r1 = 7
r2 = 5

dit:
d=.....?

Jawab:
d² = p²–(r1+r2)²
= 20² – (7+5)²
= 400–(12)²
= 400–144
d²= 256
d = √256 = 16cm (D)