# Absolute value graph

• May 4th 2009, 03:35 PM
mathprob
Absolute value graph
ABS(2x + y) - ABS(x + 3y) = 8

ABS = absolute value

I need to know where to start
• May 4th 2009, 04:30 PM
VonNemo19
$\mid2x+y\mid-\midx+3y\mid=0$

This is what we wish to solve. $\mid2x+y\mid-\midx+3y\mid=0$

We first must recognize that $\mid2x+y\mid=2x+y$ or $-(2x+y)$ . So, knowing this, can you finish up?
• May 4th 2009, 04:43 PM
mathprob
Quote:

Originally Posted by VonNemo19
$\mid2x+y\mid-\midx+3y\mid=0$

This is what we wish to solve. $\mid2x+y\mid-\midx+3y\mid=0$

We first must recognize that $\mid2x+y\mid=2x+y$ or $-(2x+y)$ . So, knowing this, can you finish up?

it says latex error in your first two lines, idk why
• May 4th 2009, 05:31 PM
VonNemo19
When dealing with absolute value, you have to be aware of the folling fact-that $\mid{x}\mid=\mid{-x}\mid=x$ So, therefore $x$ can have 2 different values, but the corresponding value of $y$, or $f(x)$ will have only one. So knowing that....

We've got to set up different possibilities for the given expressions.

$\mid2x+y\mid=\pm(2x+y)$ and $\mid{x+3y}\mid=\pm(x+3y)$.

So, with this, can you take it from here?
• May 4th 2009, 05:39 PM
VonNemo19
$\sqrt{a^2+b^2}$
• May 4th 2009, 05:45 PM
mathprob
i dont really know what you want me to do? what do i do after i get +- ?
what does the square root formula have to do with this
• May 4th 2009, 05:51 PM
VonNemo19
Solve for y for the different possibilities and then plot your graph.

Pythagoras has nothing to do with this. I was showing my brother how to type in math code.(Wink)
• May 4th 2009, 05:53 PM
mathprob
Quote:

Originally Posted by VonNemo19
Solve for y for the different possibilities and then plot your graph.

Pythagoras has nothing to do with this. I was showing my brother how to type in math code.(Wink)

so we do
2x + y = 8
-2x - y = 8
x + 3y = 8
-x-3y = 8

what do we do with the |2x + y| - |x + 3y| = 8
what do we do with the - sign in the middle

BTW this graph is on a coordinate plane, not on a number line
• May 4th 2009, 06:11 PM
VonNemo19
It stays right were it is. you leave everything the same but the two expressions in the inequality signs
• May 4th 2009, 06:16 PM
mathprob
Quote:

Originally Posted by VonNemo19
It stays right were it is. you leave everything the same but the two expressions in the inequality signs

? i have no idea what youre talking about

is it this
2x + y - x - 3y = 8

and you also do the other 3 possible equations and just set em equal to y and graph?

Anyone can help? due tommorow :(