# Logarithm equation

1. Oct 18, 2004

### vt33

I need to solve 7^2x - 5*7^x - 24 =0. Am I on the right track by starting with 7^2x - 35^x - 24 = 0?

2. Oct 19, 2004

### Tide

Let $y = 7^x$ and see where that leads! :-)

3. Oct 19, 2004

### vt33

?

I sorry, can elaborate. Are you talking about ax+by+c=0. If so, I'm still a little confused.

4. Oct 19, 2004

### Tide

You did say "logarithm equation" in the title so I assumed you meant you want to solve this equation:

$$7^{2x} - 5 \times 7^x - 24 = 0$$

If so then set $y = 7^x$ and since $7^{2x} = \left(7^x\right)^2$ your equation becomes

$$y^2 - 5y - 24 = 0$$

which you can easily solve for y from which you can obtain x.