If two sides of a triangle are 5 and 7, the third side could be?

Question

If two sides of a triangle are 5 and 7, the third side could be

1

2

4

12

Answer 1

Let a and b measures of two sides of a triangle.
Possible measures, x, for the third side are
| a - b | < x < a + b.

In this triangle,
| 5 - 7 | < x < 5 + 7
2 < x < 12

Answer: 4 is the measure of the third side.

Answer 2

4

Answer 3

Only 4 satisfies that rule that the sum of any two sides of a triangle must be greater than the 3rd side.