For every positive integer n, prove that `7^n-3^n`is divisible by 4.

Explanation

`7^n - 3^n = 4t`

a) `n=1`

b) `n=k, n=k+1`

a) n=1, LHS`7^n - 3^n= 7-3 = 4`

RHS`= 4`

b) Assumption `n=k`

`7^n - 3^n = 4k`

`n= k+1`

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