How do I solve the followinf equation using the elmination method?

p = 28 +q

3p = -9q+120

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- Oct 20th 2008, 10:38 AM #1

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- Oct 20th 2008, 10:52 AM #2
First rewrite it as

$\displaystyle \begin{array}{rcrcr}p&-&q&=&28\\3p&+&9q&=&120\end{array}$

I noticed that if you divide the second equation through by 3, you end up with this system:

$\displaystyle \begin{array}{rcrcr}p&-&q&=&28\\p&+&3q&=&40\end{array}$

I would like to eliminate p. Thus, multiply the first equation by -1 and then add the equations together:

$\displaystyle \begin{array}{rcrcr}-p&+&q&=&-28\\p&+&3q&=&40\end{array}\implies 4q=12\implies \color{red}\boxed{q=3}$

Can you find p?

--Chris

- Oct 20th 2008, 10:55 AM #3

- Oct 20th 2008, 11:10 AM #4

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- Oct 20th 2008, 11:22 AM #5

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