Posted by Bob on Wednesday, January 30, 2008 at 10:49pm.
I need to make a formula showing that I added 100 to the 99th Triangular Number..
Anyone know how I can do that?

Math  drwls, Wednesday, January 30, 2008 at 11:23pm
99th triangle number = N(N+1)/2 = 4950
Adding 100 to it gives you
4950 + 100 = 5050.
That happens to be the 100th triangle number:
100*101/2