In this case, the Triangle Inequality Theorem is used. Basically, just add up the pairs:
9 and 7
9 and 16
7 and 16
Make sure when you add them up, the sum of the two sides is greater than the other side. Unfortunately, this is not true because 9 + 7 = 16. In order for this to have been true, the two sides would have had to equal a number greater than 16, not equal to.
