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

1. 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.

2. 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:

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

Now, graph the lines, and look back at your original inequalities. The first inequality is the entire region above and AT the line $y=2x-3$. The second region is the entire region below the line $y=-4x-5$. 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.

3. 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?

4. 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?

Close.... $y<-4x-5$ would be the region to the left of the line.

5. 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?

6. 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?
$9x+7y > -21$

$7y > -21 - 9x$

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

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