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I'm trying to understand my textbook's example (it's part of a mathematical induction problem) and I just don't get how the author managed to simplify this formula:

$$\frac{(k-1)(k-1 +1) (2(k-1)+1)}6 = \frac{(k-1) k(2k - 1)}6$$

Could anyone explain in simple steps how they got from the left hand to the right hand? My math skills are very basic.

Thanks

3 Answers 3