Question 1200167
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Treat 109 as 100+9


The task of computing 109^2 is the same as (100+9)^2


Then use the identity
(a+b)^2 = a^2 + 2ab + b^2
where 
a = 100
b = 9
I'll let the student perform the computation.


A similar example:
27^2 = (20+7)^2
27^2 = 20^2 + 2*20*7 + 7^2
27^2 = 400 + 280 + 49
27^2 = 680 + 49
27^2 = 729
You can use a calculator to confirm.
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