5.1.1

[STARTS AT 4:45]

Instructor:  1/5, negative 1/7, 1/9, negative 1/11. All right, so the denominators, I see a pattern. The numerators, they are just-- the numerators are simply going between 1 to negative 1, 1 to negative 1. 

So let's do a negative 1 to the n. And if I plug in a value of 1, that would be negative. Maybe I should make that an n minus 1. Let's try that. 

If I plug in a value of n equals 1, that is positi-- yeah, that's positive. If I plug in a value of 2, that is negative. OK, so it's alternating back and forth properly. 

Now, the denominator is 5 plus-- and it is increasing by 2, so 2 times n minus 1. So let's write that as negative 1 to the n minus 1 over 2n plus 3. That is our explicit formula for that sequence.

[ENDS AT 5:48]