# Simultaneous equation of two Graph line equations.?

• Oct 21st 2009, 04:54 AM
Simultaneous equation of two Graph line equations.?
Hi, i have two graphs
One that is Price against Demand. this has the line equation of
P(price) = 21 - 3/2 d (demand)

the second graph is price against supply which has the line equation of
P = 2S ( supply) + -7

Now then what i need to know how to do is, how to find out the price at which SUpply and demand are the same, by using a Simultaneous equation. I already know its 9 by putting them on the same graph but i need to do it with a Simultaneous equation thanks.

the actual question is.
By solving a set of two simultaneous equations find the price at which supply is equal to demand. What is the demand at such a price?
• Oct 21st 2009, 06:22 AM
CaptainBlack
Quote:

Hi, i have two graphs
One that is Price against Demand. this has the line equation of
P(price) = 21 - 3/2 d (demand)

the second graph is price against supply which has the line equation of
P = 2S ( supply) + -7

Now then what i need to know how to do is, how to find out the price at which SUpply and demand are the same, by using a Simultaneous equation. I already know its 9 by putting them on the same graph but i need to do it with a Simultaneous equation thanks.

the actual question is.
By solving a set of two simultaneous equations find the price at which supply is equal to demand. What is the demand at such a price?

When supply=demand put supply=demand=x, then you want a solution of the equation:

21 - (3/2) x=2x -7

which represents the equality of the supply and demand at price x.

CB