Prove that: For all integers n, 21| (3n^7 + 7n^3 + 11n). @MIT 18.01 Single …
it works for n=1 21|21 ---- assume it is true for some k and now you have to show it is true for k+1
for some integer k* for some integer l 21l=3k^7+7k^3+11k now we want to show there is some integer m such that 21m=3(k+1)^7+7(k+1)^3+11(k+1)
See attached solution
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