Let the 3 sides of a triangle be a,b and c
For it to be a triangle then
a + b > c , a + c > b , b + c > a
12 , 12 , 20
12 + 12 > 20
24 > 20
12 + 20 > 12
32 > 12
Hence is a triangle
10,3,7
3 + 7 .....10
10 = 10
Hence is not a triangle since it does not satisfy the rules above
7,7,11
7 + 7 .... 11
14 > 11
11 + 7 ..... 7
18 > 7
Hence the figure formed is a triangle
24,9,12
9 + 12 .... 24
21 < 24
Hence is not a triangle
The rule is that for 3 numbers to form the sides of a triangle then the sum of any 2 of the numbers should be equal to the third