An Algebra 1 Question

• Sep 17th 2008, 02:24 PM
Rocker1414
An Algebra 1 Question
Hello all, thank you for your time.

Solve the system:

-x+3y=-1
x+2y=4

I understand how to do this, but my answer was not correct, the book said the answer was:
(14/5,3/5) but I have no idea how it got that. I must have made an error in my work, but I'm not sure where.

I started with x+2y=4 Subtracting 2y makes x=4-2y

Then you plug that into the other equation and you get

-4-2y+3y= -1
Which simplifies to:
-4+y=-1
y=3
Plugging that into the other one:
x+2x3=4
Which simplifies to:
x+6=4
Subtract six:
x=-2

Which gives an answer of (-2,3) but I know this is not corrrect because it does not work when you plug that into x and y for the original two sets.

Where am I making my error here?

Thank you very much
• Sep 17th 2008, 02:29 PM
icemanfan
You made your error on the first step. Given \$\displaystyle x = 4 - 2y\$ and \$\displaystyle -x + 3y = -1\$, you can substitute for x into the second equation: \$\displaystyle -(4 - 2y) + 3y = -1\$. This gives you \$\displaystyle -4 + 2y + 3y = -1\$, or \$\displaystyle 5y - 4 = -1\$.
• Sep 17th 2008, 04:34 PM
Rocker1414
Okay, just to make sure, same kind of problem with the -x thing i messed up

Write the equation of the line that is parallel to line A and passes through Point P

Line A=

\$\displaystyle y= -x+4\$

Point P= (-1,2)

That would be:
\$\displaystyle y=-2-b\$ right?
Originally it would be +b (y=mx+b) but since it's -x the + changes to a - correct?
If so, it would be
\$\displaystyle 2=-2-b\$
\$\displaystyle 4=-b\$
\$\displaystyle 4=b\$

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

correct?
• Sep 17th 2008, 04:52 PM
Rocker1414

At the end I wrote

\$\displaystyle 4=-b\$
then
\$\displaystyle -4=b\$
so
\$\displaystyle y=2x-4\$

Forgot the negative on the second one(Doh)
• Sep 17th 2008, 10:49 PM