# Solving a delta epsilon proof given a graph

• Sep 15th 2010, 03:08 PM
penguinpwn
Solving a delta epsilon proof given a graph
My professor started covering these today and i have never seen them before, even though I took a high school calculus class. How do I go about solving this?

(Problem attached)
• Sep 16th 2010, 01:07 AM
tom@ballooncalculus
You can read the first part of the condition as,

"if the distance of x from 5 is less than delta",

and the second part as,

"then the distance of y from 3 is less than 0.6".
• Sep 16th 2010, 04:10 AM
HallsofIvy
This problem is actually much easier than if you are given a formula for the function and you really need to understand it.

"3.6" and "2.4" are 3+ .6 and 3- .6 so the two horizontal red lines on your graph show the boundaries for "\$\displaystyle |f(x)- 3|< .6\$". In order that f(x) be within those two lines x must be within the two vertical red lines. Those are at 4 and 5.7 which are different distances from 5: |4- 5|= 1 and |5.7- 5|= .7. But since .7< 1, if |x- 5|< .7 certainly |x- 5|< 1 will also be true. So we stay within the two vertical red lines, and so the function value is with in the two horizontal red lines as long as |x- 5|< .7.