A triangle has two sides of lengths 4 and 5? What is the value of the third side?

It would be 20 given the formula A=BH.

The triangle inequality theorem states that the sum of any two sides of a triangle must be greater than the third side.

You can write this as a formula: A + B > x, where x is the third side.

A + B > x

4 + 5 > x

9 > x or x < 9

A + x > B

4 + x > 5

x > 1

B + x > A

5 + x > 4

x > -1

Given two side lengths 4 and 5, the third side must be between 1 and 9.