Answer:
Triangle Inequality Theorem
see the explanation
Explanation:
see the attached figure to better understand the problem
we know that
The Triangle Inequality Theorem states that the sum of any 2 sides of a triangle must be greater than the measure of the third side
In the triangle ABC of the figure
Applying the Triangle Inequality Theorem
1) First case

solve for x
Combine like terms left side

Rewrite

2) Second case

solve for x
subtract 8 both sides


therefore
The range of possible lengths of the third side AB is the interval (2,18)
All real numbers greater than 2 units and less than 18 units