Prove that 2 + 5 + 8...+ (3n -1) = (1/2)n(3n+1) for all n N.

Seems to only work for the base case. Can this be proved by induction?

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- October 15th 2009, 08:05 AMp00ndawgInduction proof help
Prove that 2 + 5 + 8...+ (3n -1) = (1/2)n(3n+1) for all n N.

Seems to only work for the base case. Can this be proved by induction? - October 15th 2009, 09:02 AMMush
Another way to write this is as follows:

Prove that

To prove this by induction, see if it works for the base case of

, thus base case holds.

The next step is to ASSUME the rule holds for k. Take it for granted that:

Now, using this result, try to prove that the rule also holds for k+1.

Here's a tip: