In any triangle, a side is longer than the difference between the other two. A side is also less the the sum of the other two. If these two rules are not obeyed then a triangle cannot be formed by those sides.
a = 7 cm. b = 3 cm.
Then c > 7-3 = 4 cm and also, c < 7+3 = 10 cm.
4 cm < the third side < 10 cm
