# Homework Help: Finding the value of an integral given a graph

1. Jan 31, 2012

### turbokaz

1. The problem statement, all variables and given/known data
http://tinypic.com/view.php?pic=1xa2f&s=5 (this shows the graph that is related to the problem)
is the graph of an anti-derivative, F, of a
function f, use this graph to determine the value of I=∫ from 0 to 8 |f(x)|dx.
value of the deﬁnite integral

2. Relevant equations

3. The attempt at a solution
The answer choices are 11, 12, 13, 14, or 15. I have no idea how to get these answers. I looked at the graph and used Reimann Sum technique of counting up the squares, but I get numbers in the 20's. For absolute value functions, I know you switch any negative values to positive, but this whole function looks positive to me? Thoughts?

2. Jan 31, 2012

### ehild

Hi turbokaz,

The plot is the antiderivative already, no need to integrate it further.
How do you calculate the definite integral between two points from the antiderivative?

What do you think about the sign of f(x)? In what domain is it positive and where is it negative?

ehild

3. Jan 31, 2012

### turbokaz

F(b)-F(a)?
F(b) is 1, F(a) is 2. 1--2=3?

4. Jan 31, 2012

### turbokaz

Bump...I'm still not getting anywhere

5. Jan 31, 2012

### turbokaz

Nevermind. I understand the problem now. The answer is 11.

6. Jan 31, 2012

### ehild

Congratulation!

ehild