Q. Find whether each of the following numbers is a perfect square or not?
(i) 121
If it is a sum of successive odd natural numbers starting with 1, then it is a perfect square.
So we try to express 121 in successive integers. This can also be done by subtracting successive odd natural numbers from 121.
Applying the concept :-
121 - 1 = 120
120 - 3 = 117
117 - 5 = 112
112 - 7 = 105
105 - 9 = 96
96 - 11 = 85
85 - 13 = 72
72 - 15 = 57
57 - 17 = 40
40 - 19 = 21
21 - 21 = 0
Thus 121 is a perfect square.