# Limits question

1. Aug 28, 2005

### kendal12

I just started calculus and we are doing limits. I was doing fine on my hmwrk until i came to this problem:

Find lim f(x+∆x) – f(x)/ ∆x
∆x→0

f(x)= x^2 – 4x

I have no idea what the delta means... I know in chem it means "a change in", but I don't know what to do with it here. My book doesn't explain it either. Please help! Thanks

2. Aug 28, 2005

### mathmike

delta x ->0
means as x approaches zero

or in other words the change in the value of x is getting so small that it is almost zero.

3. Aug 28, 2005

### kendal12

oh so it changes nothing?

4. Aug 28, 2005

### kendal12

or what am i supposed to do with the delta x value?

5. Aug 28, 2005

### Tide

kendal,

I seriously doubt that. For purposes of solving your problem and to get you accustomed to the concept why don't you just replace the $\Delta x$ with something more friendly looking like a? Then you can carry out your algebra and examine what happens when a is made arbitrarily small.

6. Aug 28, 2005

### kendal12

Trust me. I have read the entire chapter looking for something explaining the delta and there is nothing. Thanks for the tip though.

7. Aug 28, 2005

### kendal12

ok, so I worked out the problem and got 2x+a... is this correct? For some reason I dont think it is, but I thought I worked it out right...

8. Aug 29, 2005

### Tide

You should have gotten $2x - 4 + a$. Recheck your algebra.