Solve the system

• Jan 24th 2013, 05:47 PM
Oldspice1212
Solve the system
Solve the system by using elementary row operations on the equations. Follow the systematic elimination procedure.

3x1 + 6x2 = 6
4x1 + 7x2 = 11

Ok so first I multiply each entry in row 1 by 1/3 to get 1 in the first column in row 1.

Making it

1 2 2
4 7 11

Then I multiply by -4 and add to get row 2 column 1 to = 0

So

1 2 2
0 -1 3

Then I multiply each entry in row 2 by -1 to make it positive

there it's

1 2 2
0 1 -3

Now I multiply each entry in row 2 by -2 and add it to row 1 to make column 2 in row 1 a 0.

Now it's

1 0 -4
0 1 -3

x1 = -4
x2 = -3

3(-4)+6(-3) = -30
4(-4)+7(-3) = -37

Where did I go wrong? >.<

• Jan 24th 2013, 05:51 PM
Prove It
Re: Solve the system
OK, before we continue, you always write down the ENTIRE system after each step, not just one side of it. All operations need to be done to both sides of each equation after all.
• Jan 24th 2013, 05:55 PM
Oldspice1212
Re: Solve the system
I think I did that lol just looked over it again I'm getting the same answer?
• Jan 24th 2013, 06:29 PM
Prove It
Re: Solve the system
Oops, I misread what you wrote, sorry. When you got to

\displaystyle \displaystyle \begin{align*} \begin{matrix} 1 & 2 & \phantom{-}2 \\ 0 & 1 & -3 \end{matrix} \end{align*}

and multiplied each term in Row 2 by -2 and added to row 1, you should actually have gotten

\displaystyle \displaystyle \begin{align*} \begin{matrix} 1 & 0 & \phantom{-}8 \\ 0 & 1 & -3 \end{matrix} \end{align*}
• Jan 24th 2013, 06:46 PM
Oldspice1212
Re: Solve the system
Yeah I just got it lol :) I noticed it right after I left the site on my sheet I multiplied -2 by 3 which gave me -6 and messed up everything when indeed it was -2 * -3 :P, thanks though!

3(8)+6(-3) =6
4(8)+7(-3) = 11