Editing Difference of two squares (section)

===Difference of two ''n''th powers===
[[File:Difference_of_squares_and_cubes_visual_proof.svg|thumb|Visual proof of the differences between two squares and two cubes]]
If {{mvar|a}} and {{mvar|b}} are two elements of a commutative ring, then<ref>{{cite book |last=Grigorieva |first=Ellina |title=Methods of Solving Nonstandard Problems |isbn=978-3-319-19886-6 |doi=10.1007/978-3-319-19887-3_2 |publisher=Birkhäuser |at=Eq. 2.13, {{pgs|83}} |year=2015 }}</ref>

<math display=block>a^n-b^n=(a-b)\biggl(\sum_{k=0}^{n-1} a^{n-1-k}b^k\biggr).</math>

The second factor looks similar to the [[binomial theorem|binomial expansion]] of <math>(a+b)^{n-1}</math>, except that it does not include the [[binomial coefficient]]s {{tmath|\tbinom{n-1}{k} }}.