Since this is a right triangle, the Pythagorean Theorem can be used to find the missing side length. The Pythagorean Theorem is a² + b² = c², where c is the hypotenuse of the triangle.
The error is that the numbers were plugged into the theorem incorrectly - the hypotenuse is the side opposite the right angle (in this case, it is 8 ft). That means the c in a² + b² = c² should be substituted with 8, like so:
a² + b² = c²
6² + b² = 8²
Now that the numbers are substituted correctly, you may solve for the third side.
6² + b² = 8²
36 + b² = 64
b² = 28
b ≈ 5.29
Answer:
The third side length is approximately 5.3 feet.