
Using Binomial Expansion here!
Key Idea: (a+b)^n -> When we expand this, every single term except the last term (b^n) will contain "a".
For example ->
(a+b)^2 = a^2 + 2ab + b^2
(a+b)^3 = a^3 + 3a^2b + 3ab^2 + b^3
Observe - every term except the last one contains an a.
How does this help?
Say, if we need to find the remainder 29^243 is divided by 7.
29^243 = (28+1)^243
So, in the expansion of the above -> every single term except 1^243 will contain "28".
(28+1)^243 = 28a + 28b + .... + 1^243
And given that 28 is a multiple of 7, all these terms will give a remainder of 0. This means that what remains is 1^243.
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In the given question, one way to solve this question is to try and express the number (say 333) in the format of 7k +/- something, and simplify, step by step.
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Harsha
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