00:01
Okay, here we're looking at some triangle numbers.
00:03
In our triangle numbers, we are creating this triangle by alternately stacking, and we have three on the bottom as our end value, and our total number, 1, 2, 3, 4, 5, 6 is the actual triangle number.
00:17
So here we have 4 on the bottom row with a total of 10.
00:21
And we want to know how many are going to be on the bottom row if the total number here is 820.
00:28
So we're going to plug in.
00:31
We have 820 equals n times n plus 1 over 2.
00:38
Let's multiply both sides by 2 to get rid of this fraction.
00:42
So we end up with 1640.
00:45
I'm going to go ahead and distribute this as well.
00:47
So we have n squared plus n...