Answer:
D
Explanation:
Following Pythagorean Theorom, we know a^2 + b^2 = c^2. We know b and c. a^2 + 5^2 = 13^2.
a^2 + 25 = 169
a^2 = 144
a = √144
a = 12
So, the answer is 12, which means we pick D
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