The triangle inequality says any two sides add up to more than the third side. Â We only ever have to check that the two smaller sides are more than the biggest side. Â
1) 12, 12, 12
YES. Â
Sure, it's an equilateral triangle.
2) 6, 11, 13
6+11>13 YES
3) 11, 12, 16
11+12>16 YES
4) 7, 8, 18
7+8<18 NO
5) 6, 12, 21
6+12<21 NO
6) 7, 10, 7
7+7>10 YES
7) 8, 7, 1
1+7=8 That's called a degenerate triangle, vertices three collinear points. Â A degenerate triangle is not a triangle. Â NO
8) 11, 22, 9
9+11<22 NO
9) 10, 6, 3
3+6<10 NO
10) 10, 19, 7
10+7<19 NO
11) 6, 5, 6
5+6>6 YES
12) 6, 3, 12
6+3<12 NO
13) 7, 4, 6
4+6>7 YES
14) 13, 7, 9
7+9>13 YES