12 cm, 7 cm, 5 cm will not make a triangle. Here’s why: 12+7 is greater than 5 (that’s good) 12+5 is greater than 7 (that’s good) 7+5 is equal to 12. That is not good because the 2 opposite sides must add together to be greater than the third side, in this case 12. If the 2 sides are less than or equal to the third side, then the triangle will not be formed. I hope this helps, and good luck.
