Since the perimeter must not exceed 291.
Let the third side be x.
x + 87 + 64 < 291
x + 151 < 291.
x < 291 -151.
x < 140. (First)
But for a triangle there is what is called the Triangle Inequality Theorem. That given the two sides of a tringle, the third side of the triangle must greater than the positive difference between the two sides and less than the sum of the two sides.
So for this case. 87 and 64.
x > ( 87 - 64). x > 23.
x < (87 + 64) x < 151. Combine both inequalities.
23 < x < 151 (second).
Combining First and second. Both must be satisfied.
So we have a more accurate answer as:
23 < x < 140. x is greater than 23 and x is less than 140.
x could be 24, 25, 26, 27, ......, 139. cm.
I hope this helps.
