# Help with delta epsilon proofs...

• Jan 6th 2009, 11:32 AM
bemidjibasser
Help with delta epsilon proofs...
I need to prove that lim (mx+b) as x approaches c = mc +b. Any tips or help would be greatly appreciated.
Also, What exactly is the relationship of the definite integral to the derivative?
Again, help and or tips would be greatly appreciated.
• Jan 6th 2009, 12:09 PM
Moo
Hello,
Quote:

Originally Posted by bemidjibasser
I need to prove that lim (mx+b) as x approaches c = mc +b. Any tips or help would be greatly appreciated.
Also, What exactly is the relationship of the definite integral to the derivative?
Again, help and or tips would be greatly appreciated.

For the second one, if f is a function and f ' is its derivative, we have :

$\displaystyle \int_a^b f'(x) ~dx=f(b)-f(a)$

Usually, we define an antiderivative of f, F and say $\displaystyle \int_a^b f(x) ~dx=F(b)-F(a)$

Since f is an antiderivative of f ', we have the formula above.
• Jan 6th 2009, 12:12 PM
galactus
This actually is not that bad. I know that the epsilon-delta thing can be confusing.

$\displaystyle f(x)=mx+b, \;\ m\neq 0$

$\displaystyle \lim_{x\to c}(mx+b)=mc+b$

$\displaystyle |(mx+b)-(mc+b)|<{\epsilon}$

$\displaystyle |m(x-c)|<{\epsilon}$

$\displaystyle |x-c|<\frac{\epsilon}{|m|}={\delta}$

Therefore, for $\displaystyle {\epsilon}>0$, let $\displaystyle {\delta}=\frac{\epsilon}{|m|}$
• Jan 6th 2009, 03:41 PM
bemidjibasser
Thank you both. Is there a way to expand on the relationship of the derivative and the definite intergal? I think I can follow the formulas above, but how would you go about explaining more in words? Thanks again for help.
• Jan 6th 2009, 05:02 PM
Mathstud28
An alternative to Moo's post would be that in a sense integration and differentiation are inverses. If $\displaystyle F(x)=\int_{a}^x f~dx$ and $\displaystyle f$ is continuous at some point $\displaystyle x_0$ then $\displaystyle F(x)$ is differentiable at $\displaystyle x_0$ and $\displaystyle F'(x_0)=f(x_0)$
• Jan 6th 2009, 05:35 PM
bemidjibasser
Does the fundamental theorem have anything to do with this? Or the mean value theorem? Thank you again...
• Jan 6th 2009, 05:45 PM
Mathstud28
Quote:

Originally Posted by bemidjibasser
Does the fundamental theorem have anything to do with this? Or the mean value theorem? Thank you again...

These are the fundamental theorems of calculus (what me and Moo gave)