Determine if the given sides are a triangle or not

A. 21 cm, 7 cm, 6 cm

This is not a triangle

Step-by-step explanation:

If you use the triangle inequality theorem you can reach your answer.

The theorem states that if you add the length of any 2 sides together, you will have a length greater than the length of the other side. Using this method we can easily see that 7+6=13 which is less than 21. Meaning this is not a triangle