Algebra: solving -5x + 1 > 11, finding slope, y-int. of....

Mixmaster

New member
Joined
Jan 10, 2008
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1
Need help with refresher on problems:

1. -5x+1>11

2. solve 5x+4y=12 for y
slope=?
y-intercept=?

Thanks Mixmaster...
 

Mrspi

Senior Member
Joined
Dec 17, 2005
Messages
2,128
Re: Algebra

Mixmaster said:
Need help with refresher on problems: -5x+1>11
also solve; 5x+4y=12 for y
slope=?
y-intercept=?

Thanks Mixmaster...
For your first problem, remember that solving an inequality is pretty much (with ONE notable exception) the same as solving an equation.

You've got

-5x + 1 > 11

You want to get the variable term by itself on one side. To eliminate the +1, add -1 to both sides of the inequality:

-5x + 1 + (-1) > 11 + (-1)

-5x > 10

Now, to get 1x, or just x, on the left side, you need to divide both sides by -5 to "undo" the multiplication by -5. Here's the BIG difference between equations and inequalities. If you multiply or divide both sides of an inequality by a NEGATIVE number, then you need to REVERSE the direction of the inequality symbol. So, we'll divide both sides by -5, and we will switch > to <:

(-5x) / (-5) < (10) / (-5)

x < -2

Now check....is the original inequality true when x is any number less than -2?

Your second problem asks you to solve

5x + 4y = 12

for y.

Solving for y means getting y by itself on one side of the equals sign.

Add -5x to both sides of the equation to get rid of the 5x that's there with the y term:

5x + 4y + (-5x) = (-5x) + 12

Combine like terms:

4y = (-5x) + 12

Now, you've got 4y, but you want 1y or just y. So, you'll need to divide both sides of the equation by 4:

(4y) / 4 = (-5x) / 4 + (12/4)

y = (-5/4)x + 3

This is in "slope-intercept form" or y = mx + b. When the equation of a line is in this form, "m" is the slope of the line. So...you should be able to see what the slope is.

If you're still having trouble, please repost, showing ALL of the work you've done to solve this problem.
 
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