







Finite differences 
20030210 

Jenny pose la question :
I need to find a formula that will work with any number. I am finding the volume of a 3d cross shape. Here are my results so far:
Term Number 0 1 2 3 4 5
nth term 1 7 25 63 129 231
1rst diff 6 18 38 66 102
2nd diff 12 20 28 36
3rd diff 8 8 8
I can't seem to find a formula that will work with any number. Any help would be much appreciated. Penny Nom lui répond. 





Arithmetic sequences 
20010910 

Rachel pose la question : I can't seem to figure out a problem that deals with arithmetic sequencing. This is the question: The 5th term in an arithmetic sequence is 1/2, and the 20th term is 7/8. Find the first three terms of the sequence. I attempted this problem with the formula: An = a + (n1)d (where the n represents the nth term, a is the first term, and d represents the common difference) I keep getting 9.5 for the first number, and then 3/120 as the common difference between the numbers. But as I have figured it, the sequence is getting greater and greater, and my data does not go with the terms given. Penny Nom lui répond. 





Geometric and arithmetic sequences 
20010126 

Garry pose la question : what are the equations for geometric and arithmetic sequences? also, what are the equations for finding the sums of those series? Leeanne Boehm and Penny Nom lui répond. 





The sum of the squares of 13 consecutive positive integers 
20000825 

Wallace pose la question : Prove that it is not possible to have the sum of the squares of 13 consecutive positive integers be a square. Harley Weston lui répond. 

