Suppose you have an n × n square. Give two equivalent expressions that express the number of unit squares that have an edge on the boarder of the larger square.
As we can see from solution E, the sequence generated by the border problem is arithmetic sequence starting at n = 2 with initial value a2 = 4 and common difference d = 4.
Suppose you have an n × n × n cube. Give two equivalent expressions that express the number of unit cubes that have a face on the outside surface of the larger cube.
Is the sequence generated by finding the number of unit cubes with a face on the surface of the n cube an arithmetic sequence? What are some of the ways we can tell?
If we look at the first few cubes, we start with 8, then 26, then 56. The first two differences are 26 – 8 = 18 and 56 – 26 = 30.
We can also tell due to the square in the fully simplified expression that shows the closed form for the sequence is not linear.