1.

72n – 32n is divisible by 4.

Answer»

Let P(n): 7n  – 3n  is divisible by 4.

For n = 1, P(1): 71  – 31  = 4 which is divisible by 4.

∴ P(1) is true. 

Let us assume P(k) is true for some k∈N 

i.e., 72n – 32n is divisible by 4. 

Thus, P(k) ⇒ P(k +1). 

Hence, by mathematical induction P(n) is true for all n∈N



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