00:02
All right.
00:03
So what we know is that in 2006, the revenue was $49 .3 billion.
00:09
And by 2013, it was $20 .7 billion.
00:14
And we know that it's decreasing according to the exponential decay model.
00:19
So we need to find the value of k and write our function.
00:23
So our general format is that a is equal to a sub 0e to the kt.
00:30
So we know that by 2013, this had been seven years.
00:39
So we're going to substitute in our values here.
00:41
This is going to be our a, and this is going to be our a sub -zero, since we're basing it on 2006.
00:52
So 20 .7 is equal to 49 .3e to the k times seven, again, because it had been seven years.
01:04
So we can solve this for k first, dividing by 49 .3 on both sides.
01:18
20 .7 divided by 49 .3 is 0 .4199 equals e.
01:27
And i'm going to write that as 7k for my exponent.
01:32
And here, our k is up in that exponent, and we have the base of e...