00:01
Okay, this series is geometric and we can see that our common ratio is two -thirds.
00:08
The two is increasing square two cube, two four, two five, and the three is increasing three power five, three six, three seven, three eight.
00:18
So two -thirds is the ratio.
00:21
The first term, a -1, is here.
00:26
So a -1 is two squared over three power five.
00:31
Now this sum goes on forever, so i can use the formula, or sum to infinity, as a1 over 1 minus r.
00:41
And the key requirement, if and only if, minus 1 less than r or less than 1.
00:48
Well, here we're fine because r is 2 thirds.
00:51
That's the required range...