Final answer:
The length of the third side is 36 inches.
Step-by-step explanation:
To find the length of the third side of a right triangle, you can use the Pythagorean theorem.
Given that one leg is a = 15 in., and the hypotenuse is c = 39 in., you can calculate the length of the other leg, b, using the formula:
a² + b² = c²
In this case, plug in the values for a and c:
15² + b² = 39²
225 + b² = 1521
Now, subtract 225 from both sides of the equation:
b² = 1521 - 225
b² = 1296
To find b, take the square root of both sides:
b = √1296
b = 36 in.
Therefore, the length of the third side is 36 inches.