Does 12cm, 7cm, 5cm, make a triangle

No, it doesn't.

Step-by-step explanation:

In order to find what makes a triangle, lets use the Triangle Inequality Theorem!

This theorem can help us show whether the sum of two side lengths of a triangle is greater than the third side or not

Here is our formula(s):

1.) a + b > c

2.) a + c > b

3.) b + c > a.

Lets make a=12, b=7, & c=5

1.) 12 + 7 > 5

    19 > 5

2.) 12 + 5 > 7

       17 > 7

3.) 7 + 5 > 12

      10 > 12

As you can see, both numbers 1 and 2 shows to be correct but 3 is not. Therefore it doesn't make a triangle. Remember, if all the two side lengths of a triangle is greater than the third side, then it makes a triangle.