(98)^2 no calculator mental math

[math_celebrity]

Round 98 to the nearest 10. This is 100. Call this a.

Calculate b which is a - our original number:
b = 100 - 98
b = 2

We can use this formula:
(a - b)^2 = a(a- 2b) + b^2

Given a = 100 and b = 2, we have:
(100 - 2)^2 = 100(100 - 2(2)) + 2^2
98^2 = 100(96) + 4
98^2 = 9600 + 4
98^2 = 9,604