# Math Is Fun Forum

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## #1 2021-04-10 04:14:34

mathland
Banned
Registered: 2021-03-25
Posts: 438

### Find Rate of Change

Find the rate of change of the function at any number c.

f(x) = x^2/(x + 3) as x tends to c.

I need to find the limit of [f(x) - f(c)]/(x - c) as x tends to c.

lim......[(x^2)/(x + 3) - (c^2)/(c + 3)] /(x - c)
x-->c

Stuck here.

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## #2 2021-04-10 21:06:07

Bob
Registered: 2010-06-20
Posts: 9,128

### Re: Find Rate of Change

hi mathland,

If you can use algebra to get a (x-c) term at the top of that expression, then these can be cancelled out and what's left will allow you to let x tend to c.

Now you can cancel the (x-c) and simplify the rest, put x=c and you're done.

Bob

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

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## #3 2021-04-11 01:56:01

mathland
Banned
Registered: 2021-03-25
Posts: 438

### Re: Find Rate of Change

Bob wrote:

hi mathland,

If you can use algebra to get a (x-c) term at the top of that expression, then these can be cancelled out and what's left will allow you to let x tend to c.

Now you can cancel the (x-c) and simplify the rest, put x=c and you're done.

Bob

Hello Bob. How are you? I took my second vaccine of Moderna yesterday and feel sick today. Everyone told me to expect getting sick the next day. They were right in this respect. I thank for you for using algebra to simplify the original set up.
I can take it from here. No math today. Just not feeling myself. This forum is ok. I would like to see more people involved. It's good to see others participate in the Help Me forum. It's always the same people.

Last edited by mathland (2021-04-11 01:56:52)

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## #4 2021-04-11 19:19:45

Bob
Registered: 2010-06-20
Posts: 9,128

### Re: Find Rate of Change

Hello mathland,

Sorry he hear you're feeling sick.  Usually it's a sign that your immune system is working so it'll most likely pass quickly.  I had something similar with the astra zenica jab.

Best wishes,

Bob

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

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## #5 2021-04-12 10:00:21

mathland
Banned
Registered: 2021-03-25
Posts: 438

### Re: Find Rate of Change

Bob wrote:

Hello mathland,

Sorry he hear you're feeling sick.  Usually it's a sign that your immune system is working so it'll most likely pass quickly.  I had something similar with the astra zenica jab.

Best wishes,

Bob

Hello Bob.

How are you? I am feeling better today. It was just the reaction
of the second Moderna vaccine. Now, I can get back to my math studies.

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