# Summation homework problem

1. Mar 9, 2010

### thereddevils

1. The problem statement, all variables and given/known data

$$\sum^{n}_{r=1}(\lg \frac{2^r(r+1)}{r})=\sum^{n}_{r=1}[\lg 2^r+\lg (r+1)-\lg r]$$

2. Relevant equations

3. The attempt at a solution

i found the answer to be $$(2^n-1)\lg 2 +\lg (n+1)$$

Am i correct , or it can be further simplified ? Thanks .

2. Mar 9, 2010

### tiny-tim

Hi thereddevils!

Your lg(n+1) is fine, but the two-y part isn't …

how did you manage to get a 2n outside the lg ?

3. Mar 9, 2010

### thereddevils

Re: summation

Thanks , tiny tim !

oh , \sum^{n}_{r=1}\lg 2^r=\lg 2+2\lg 2+3\lg 2 +...

=\lg 2 (1+2+3+...)

=\frac{n}{2}(n+1)\lg 2

i think i see my mistake , is this correct ?

4. Mar 9, 2010

### tiny-tim

(have a sigma: ∑ and try using the X2 tag just above the Reply box )

Yes, that's all correct now!