# I need to plot these Systems of Inequalities onto a graph. Help!?

• Mar 7th 2008, 09:47 AM
eraser851
I need to plot these Systems of Inequalities onto a graph. Help!?
How can I find the coordinates to these so I can graph the lines.
y >= 2x-3
y < -4x-5

There should be two lines, right? I need help finding the coordinates for each of the lines and then how I need to shade them. Left side or right side? No idea where to start. I'm a complete idiot when it comes to algebra.
• Mar 7th 2008, 10:02 AM
colby2152
Quote:

Originally Posted by eraser851
How can I find the coordinates to these so I can graph the lines.
y >= 2x-3
y < -4x-5

There should be two lines, right? I need help finding the coordinates for each of the lines and then how I need to shade them. Left side or right side? No idea where to start. I'm a complete idiot when it comes to algebra.

When graphing them, treat the inequalities as equalities like so:

$\displaystyle y=2x-3$
$\displaystyle y=-4x-5$

Now, graph the lines, and look back at your original inequalities. The first inequality is the entire region above and AT the line $\displaystyle y=2x-3$. The second region is the entire region below the line $\displaystyle y=-4x-5$. The subspace region where both of these areas intersect is what you should leave as shaded in your graph. That region of x-values satisfies both equations.
• Mar 7th 2008, 10:09 AM
eraser851
Okay, correct me if I'm wrong.

y >= 2x-3 would have coordinates at (-2,-7) and oh lets say (3,3)

y < -4x-5 would have coordinates at (1,-9) and say (-2,3)

Would this be right?

http://img.photobucket.com/albums/v2...ther/graph.jpg
• Mar 7th 2008, 10:16 AM
colby2152
Quote:

Originally Posted by eraser851
Okay, correct me if I'm wrong.

y >= 2x-3 would have coordinates at (-2,-7) and oh lets say (3,3)

y < -4x-5 would have coordinates at (1,-9) and say (-2,3)

Would this be right?

http://img.photobucket.com/albums/v2...ther/graph.jpg

Close.... $\displaystyle y<-4x-5$ would be the region to the left of the line.
• Mar 7th 2008, 10:25 AM
eraser851
Alright, now I'm stuck on a new one.
9x + 7y > -21

Since the 'y' is in the middle, how can I make a 'y=' formula?
And how would I know which side to shade on? Left or right?
• Mar 7th 2008, 10:30 AM
colby2152
Quote:

Originally Posted by eraser851
Alright, now I'm stuck on a new one.
9x + 7y > -21

Since the 'y' is in the middle, how can I make a 'y=' formula?
And how would I know which side to shade on? Left or right?

$\displaystyle 9x+7y > -21$

$\displaystyle 7y > -21 - 9x$

$\displaystyle y > -3 -\frac{9}{7}x$

Shade to the right of the line $\displaystyle y = -3 -\frac{9}{7}x$