Exercise 21 Page 430

To find the missing side length of the triangle, we will use the Pythagorean Theorem. a^2+b^2=c^2In the formula, a and b are the legs and c is the hypotenuse of a right triangle. We are given a triangle with a=12in. and b=5 inches.

Let's substitute these values into the formula.

Since a negative side length does not make sense, we only need to consider positive solutions. Therefore, c=13 inches. This corresponds to option B.