My Math Forum  

Go Back   My Math Forum > College Math Forum > Calculus

Calculus Calculus Math Forum


Reply
 
LinkBack Thread Tools Display Modes
February 21st, 2017, 12:32 AM   #1
Member
 
Joined: Feb 2017
From: East U.S.

Posts: 33
Thanks: 0

Please teach me how to do this

The limit represents f '(c) for a function f(x) and a number c. Find f(x) and c.

lim (Δx-->0) [7-8(1+Δx)]-1(-1)/Δx

So the story is... my teacher assigns this as a homework problem that's gonna turn up on our exam tomorrow, but without going over a single problem with a triangle thing in it. I looked it up and apparently it's a "change" symbol?
Please, I really just need the steps written down on how to solve this so I can at least try to learn a little before my next exam in about 11 hours. I'm willing to try to learn, and not just looking for the answer, but I have no time...

ANY advice would be great, thanks!
nbg273 is offline  
 
February 21st, 2017, 01:49 AM   #2
Senior Member
 
Joined: Feb 2016
From: Australia

Posts: 1,285
Thanks: 439

Math Focus: Yet to find out.
The 'little triangle' is an uppercase delta in Greek. And yes, it usually means 'change in'. When you see $\Delta x$, you can say 'change in x'. Although this by itself doesn't mean much.

I can't really make out what your function is supposed to be due to some peculiar bracketing.

$\displaystyle \lim\limits_{\Delta x \rightarrow 0} \dfrac{7 - 8(1 + \Delta x)}{\Delta x}$

or,

$\displaystyle \lim\limits_{\Delta x \rightarrow 0} 7 - 8(1 + \Delta x) +\dfrac{1}{\Delta x}$???

Or something else...
Joppy is online now  
February 21st, 2017, 02:46 AM   #3
Member
 
Joined: Feb 2017
From: East U.S.

Posts: 33
Thanks: 0

Quote:
Originally Posted by Joppy View Post
The 'little triangle' is an uppercase delta in Greek. And yes, it usually means 'change in'. When you see $\Delta x$, you can say 'change in x'. Although this by itself doesn't mean much.

I can't really make out what your function is supposed to be due to some peculiar bracketing.

$\displaystyle \lim\limits_{\Delta x \rightarrow 0} \dfrac{7 - 8(1 + \Delta x)}{\Delta x}$

or,

$\displaystyle \lim\limits_{\Delta x \rightarrow 0} 7 - 8(1 + \Delta x) +\dfrac{1}{\Delta x}$???

Or something else...
Sorry, I don't know how to use the website... But

lim
Δx-->0

In the numerator of the function, I have "[7-8(1+Δx)]-(-1)" (there are brackets for some reason)

And in the denominator, I just have a "Δx"

Hopefully this clarified everything.

Last edited by nbg273; February 21st, 2017 at 03:35 AM.
nbg273 is offline  
February 21st, 2017, 03:48 AM   #4
Math Team
 
Joined: Dec 2013
From: Colombia

Posts: 6,876
Thanks: 2240

Math Focus: Mainly analysis and algebra
$$f'(c)= \lim_{\Delta x \to 0} \frac{f(c+\Delta x) - f(c)}{\Delta x}$$

$f(c+\Delta x) = 7-8(1+\Delta x)$ and $f(c) = -1$. By inspection, you can then suggest a value for $c$ and an expression for $f(x)$.
v8archie is offline  
February 21st, 2017, 04:03 AM   #5
Member
 
Joined: Feb 2017
From: East U.S.

Posts: 33
Thanks: 0

Quote:
Originally Posted by v8archie View Post
$$f'(c)= \lim_{\Delta x \to 0} \frac{f(c+\Delta x) - f(c)}{\Delta x}$$

$f(c+\Delta x) = 7-8(1+\Delta x)$ and $f(c) = -1$. By inspection, you can then suggest a value for $c$ and an expression for $f(x)$.
Sorry, I'm still confused on what f(x) is... I'm bad at math...
nbg273 is offline  
February 21st, 2017, 04:29 AM   #6
Math Team
 
Joined: Jan 2015
From: Alabama

Posts: 2,574
Thanks: 667

It looks like f(x) is intended to be f(x)= 7- 8x. Then and . So . That is, for all non-zero , .

So what is the limit as goes to 0?
Country Boy is offline  
February 21st, 2017, 05:17 AM   #7
Member
 
Joined: Feb 2017
From: East U.S.

Posts: 33
Thanks: 0

Quote:
Originally Posted by Country Boy View Post
It looks like f(x) is intended to be f(x)= 7- 8x. Then and . So . That is, for all non-zero , .

So what is the limit as goes to 0?
Ohhh, I see now. Thanks for your help!
nbg273 is offline  
Reply

  My Math Forum > College Math Forum > Calculus

Tags
teach



Thread Tools
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
please add me and teach me using MyMathForum !! MATHEMATICIAN New Users 12 August 23rd, 2013 02:23 AM
How to teach yourself... MattJ81 New Users 7 July 29th, 2011 10:17 PM
will someone teach me geometry? cameron Geometry 1 June 19th, 2009 05:35 AM
please add me and teach me using MyMathForum !! MATHEMATICIAN Calculus 0 December 31st, 1969 04:00 PM





Copyright © 2017 My Math Forum. All rights reserved.