Answer:
12
Step-by-step explanation:
Using the pythagorean theorem we have DE^2 + 5^2 = 13^2
DE^2 = 169 - 25 = 144
DE = sqrt144 = 12
Or, you could just remember the triangle 5-12-13, as it is pretty common, along with 3-4-5, 7-24-25
