# Quick question regarding partial decomposition.

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• Sep 15th 2008, 06:21 PM
redman223
Quick question regarding partial decomposition.
I was just wondering about the steps that are described here but not shown. I don't see what they mean by subtracting equation 3 from equation 1 and using that in equation 2. Could someone show me the steps that were left out?

http://i231.photobucket.com/albums/e...CHOOL/math.jpg
• Sep 15th 2008, 06:47 PM
11rdc11
They used elimanation to get rid of A and then use elimanation again to get rid of B or C
• Sep 16th 2008, 12:17 AM
Moo
Hello,

\begin{aligned} (1) ~ & 1 &=& {\color{red}\boxed{A}} &+&3B&&& \\
(2) ~ &1&=&&&-B&+&3C \\
(3) ~ &-2&=&{\color{red}\boxed{A}}&&&-&C \end{aligned}

The red boxes tell us to substract (1) from (3) or (3) from (1).
This gives $1-(-2)=A+3B-(A-C) \implies 3=3B+C \implies C=3-3B$

Substitute it in (2).
• Sep 16th 2008, 12:26 AM
11rdc11
Quote:

Originally Posted by Moo
Hello,

\begin{aligned} (1) ~ & 1 &=& {\color{red}\boxed{A}} &+&3B&&& \\
(2) ~ &1&=&&&-B&+&3C \\
(3) ~ &-2&=&{\color{red}\boxed{A}}&&&-&C \end{aligned}

The red boxes tell us to substract (1) from (3) or (3) from (1).
This gives $1-(-2)=A+3B-(A-C) \implies 3=3B+C \implies C=3-3B$

Substitute it in (2).

I tried so hard to get mine to look like that but couldn't. I just gave up and gave an explanation lol
• Sep 16th 2008, 12:29 AM
matt3D
Quote:

Originally Posted by redman223
I was just wondering about the steps that are described here but not shown. I don't see what they mean by subtracting equation 3 from equation 1 and using that in equation 2. Could someone show me the steps that were left out?

http://i231.photobucket.com/albums/e...CHOOL/math.jpg

Hey, are you in Mrs. Duncan's class? haha, I'm in here 8AM class. That is from elluminate?
• Sep 16th 2008, 02:30 AM
redman223
Lol, yeah I am in the 2:00 class. Thanks for all the replies.