Question: Substitution and Elimination View Single Post
 HelpinHere Posts: 1,062, Reputation: 747 Ultra Member #2 Aug 12, 2009, 04:22 PM
Solve by substitution or elimination.

Substitution:
Solve for any of the variables in any of the equations.
Replace that variable with its value in the unused equation.
Simplify the equation
Solve for the unknowns.

Elimination:
Decide which variable you are going to eliminate.
Use your knowledge of fractions to make the coeffecients for that variable the same number, but opposites. (one +, one -)
Add the two equations. One of the variables should disappear.
Solve for the remaining variable.
Solve for the other variable using either equation.

Examples:
$y=2x+1$
$y=x+2$

Sub:
$y=2x+1$
$y=x+2$

$y-2=x$

$y=2(y-2)+1$
$y=2y-4+1$
$y=2y-3$
$-y=-3$
$y=3$

$3=2x+1$
$2=2x$
$1=x$

Elim:
$y=2x+1$
$y=x+2$

$y=2x+1$
$-2y=-2x-4$

$-y=-3$
$y=3$

$3=x+2$
$1=x$
Now, you just do the same thing, but using your equations.
If you get stuck, post what you have gotten, and I'll help you from there.

(Please, someone correct me if I'm wrong.)