Answer:
Step-by-step explanation:
sum of any two sides > third side.
difference of any two sides < third side.
1.10,21,9
10+9=19<21 (do not form a triangle)
2.
6,10,7
6+7=13>10
6+10=16>7
10+7=17>6
10-7=3<6
10-6=4<7
7-6=1<10
so it forms a triangle.
3.
5,7,2
5+2=7
(not a triangle)
4.
5,8,9
5+8=13>9
5+9=14>8
8+9=17>5
8-5=3<9
9-5=4<8
9-8=1<5
they form a triangle.
