Answer:
Step-by-step explanation:
Given that the triangle inequality requires any two sides of a triangle together have a length greater than the third side, you want an inequality that defines the range of x.
For any assignment of sides a, b, c in a triangle, we require a+b > c.
For any of the given lengths being the third side, the inequalities are ...
All of these must be satisfied, so we must have ...
1.8 < x < 12.8
Your friend claims 1.5 is a possible third side length. The above inequality excludes that value from consideration
1.5 is not a possible value of x.