# Simultaneous equations

• Jan 9th 2008, 11:11 AM
abc
Simultaneous equations
Qs= -8+2p
Qd= -35 -4p

I have to find out hat "p" is. SO normally i would times the top one by 2 to cancel out the bottom one but its - . can i times the top by - 2 but then how can find what p is. Is there a another way to find P.

I would really appreciate your help.
• Jan 9th 2008, 11:41 AM
colby2152
Quote:

Originally Posted by abc
Qs= -8+2p
Qd= -35 -4p

I have to find out hat "p" is. SO normally i would times the top one by 2 to cancel out the bottom one but its - . can i times the top by - 2 but then how can find what p is. Is there a another way to find P.

I would really appreciate your help.

If you let $Q_s = Q_d$, then this is just a system of linear equations:

$Q_d = -8 + 2p$
$Q_d = -35 - 4p$

They equal each other, so:

$2p - 8 = -35 - 4p$
$p = \frac{-9}{2}$

Now, if d and s are just coefficients, then you solve it just like you said:

$(Dq = -8 + 2p)*2$
$+ (Sq = -35 - 4p)$
========================
$(D+S)q=-43$

$q=\frac{-43}{D+S}$

Now, plug q back into one of your equations. Has this helped you?