# Double checking and some help

• Feb 5th 2009, 02:36 PM
Jubbly
Double checking and some help
I need help with solving equations with substitution I'm stuck on problem. like

x=-4y
3x+2y=20

and

y= -x+6
3x+y=-10

Can you guys also help me double check these?

4x+y=1
y=x-9
For this I got (2,7)

5x+y=4
y=2x-3
I got (1,-1) for this

Thanks for your help!(Hi)
• Feb 5th 2009, 03:26 PM
RaphaelB30
First Problem,
x=-4y
3x+2y=20

Take the first equation and put it into the second where the "x" is.

3(-4y)+2y=20

Solve for y. You get.
-12y+2y=20
-10y=20
y=-2

Second Problem
y= -x+6
3x+y=-10

Take the first equation and put it where the "y" is on the second equation.
After all that is what "y" equals.

3x+-x+6=-10

Solve for the Problem

2x+6=-10
2x=-16
x=-8

Double Checking
It is actually (2, -7) and the second one is correct.
• Feb 5th 2009, 05:01 PM
Jubbly
Quote:

Originally Posted by RaphaelB30
First Problem,
x=-4y
3x+2y=20

Take the first equation and put it into the second where the "x" is.

3(-4y)+2y=20

Solve for y. You get.
-12y+2y=20
-10y=20
y=-2

Second Problem
y= -x+6
3x+y=-10

Take the first equation and put it where the "y" is on the second equation.
After all that is what "y" equals.

3x+-x+6=-10

Solve for the Problem

2x+6=-10
2x=-16
x=-8

Double Checking
It is actually (2, -7) and the second one is correct.

Thanks for your help! Now putting them in ordered pair, would the first one look like (-8,2) and the second look like (8,-2)?
• Feb 8th 2009, 06:03 PM
RaphaelB30
Quote:

Originally Posted by Jubbly
Thanks for your help! Now putting them in ordered pair, would the first one look like (-8,2) and the second look like (8,-2)?

Yes, that's what it would look like.