# Expanding log(a+b)

1. Nov 2, 2005

### Saoist

anyoen know how to expand this? i can't think of any obvious way...

2. Nov 2, 2005

### mathman

What kind of result are you looking for - functions of a and b separately? As it stands, it is as simple as possible.

3. Nov 2, 2005

### CRGreathouse

There's not much you can do. In some cases, it's useful to factor it as $$\log a+\log(b+1)$$, but in general there's nothing simpler than the way you wrote it.

4. Nov 2, 2005

### Saoist

i have a deceptively simple question you see:

X^3 = (cY+d)^2

where c and d are constants, with x and y the variables. how would you plot the 2 variables as a straight line graph. i'm having an idiocy attack and can only think "log it...."

5. Nov 2, 2005

### Learning Curve

Take the log of Y and graph x, log y.

6. Nov 2, 2005

### Saoist

that doesn't plot that relationship as a straight line though does it?

i was under impression you had to transform [said equation] into a y=mx+c type form

7. Nov 2, 2005

### NateTG

You can't plot things like $x^3=y^2$ as a straight line on a normal graph.

8. Nov 3, 2005

### Learning Curve

I didn't mean that would give you a formula, but if you had a set of data, you could find the regression by plotting x, log y. It's not the answer but it's a way to get it.

9. Nov 4, 2005

### uart

No, none of log-log, log-linear or linear-log will make that equation a straight line.

What's the full context of the problem, do you have a number (more than 2) of x,y points and you wish to find constants c and d that give the "best fit" in some particular sense?