Given:
The lengths of two sides of an isosceles triangle are 5 and 9.
The objective is to find the length of third side.
Since we are given an isosceles triangle then the third side can be either 5 or 9 and it must satisfy the inequality given below, that is:
This is true so c can be 5.
Case 2: c = 9
Substitute this in the inequality, we have:
This is also true for c= 9
Hence, the third side can be either 5 or 9.
Thus, option A is true.