Answer:
3rd triangle can be constructed with dimensions 2,6,7.
Explanation:
sum of any two sides > third side.
difference of any two sides < third side
1.
8+5=13 not >14 (no triangle.)
2.
7+8=15 not >15 (no triangle)
3.
2+6=8>7
2+7=9>6
7+6=13>2
7-2=5<6
7-6=1<2
6-2=4<7
so it is a triangle.
4.
6+3=9 not >10 (not a triangle)