Step-by-step explanation:
The length of any side of a triangle must be less than the sum of the other 2 sides of the triangle.
Let x be the length of the 3rd side. Then we have constraints 5 + 12 > x and 5 + x > 12.
This gives 17 > x and x > 7, hence the answer is 7 < Length of the 3rd side < 17.
