1. ## Another log question

Alright, I'm trying this problem and I am completely lost. Are there any websites to understand logs? I went to the tutorial in the helpful math sites section and after I got so far into, I was really lost.

Anyways.. here's the question. Unlike the other one, I can't figure this out.

All of these have the subscript of 2.
log6-log15+log20.

I tried first dividing the 6 by 15, and then multiplying the answer by 20 and ended up with 8. However, the answer in the back is 3, so I know I'm doing something wrong? I just don't get these things...

2. Originally Posted by Chinnie15
Alright, I'm trying this problem and I am completely lost. Are there any websites to understand logs? I went to the tutorial in the helpful math sites section and after I got so far into, I was really lost.

Anyways.. here's the question. Unlike the other one, I can't figure this out.

All of these have the subscript of 2.
log6-log15+log20.

I tried first dividing the 6 by 15, and then multiplying the answer by 20 and ended up with 8. However, the answer in the back is 3, so I know I'm doing something wrong? I just don't get these things...
Hi!

$\displaystyle log_2(6) - log_2(15) + log_2(20) = log_2(\frac{6}{15}20) = log_2(8)$

So far you were right. However, you only know so far that this expression is equal to $\displaystyle log_2(8)$. Let's say $\displaystyle x=log_2(8)$, then we need to find x!

From the definition of logarithms,

$\displaystyle a^{log_a(n)} = n \Rightarrow 2^{log_2(8)} = 8 \Rightarrow log_2(8) = 3$, since $\displaystyle 2^3 = 8$