Look at the triangle inequality theorem. If it does not meet all the 3 equation requirements than the triangle can not be formed. Let me know if you need additional help
Step-by-step explanation: 6, 6, and 12 can't be sides of a triangle since 2 sides have to add up to more than the other side and can't be equal or less than. If sides 6 + 12 = 18, 18 > 6, however if 6 + 6 are added then 12=12 and will make it not a triangle.
