Do Now
Simplify each expression:
1.
(3x + y) – (2x + y)
1.
4(2x + 3y) – (8x – y)
1.
3(x + 4y) + 2(2x – 6y)
1.
(8x – 4y) + (-8x + 5y)
7-3, 7-4 Solving Linear Systems
by Elimination
OBJECTIVE: SOLVE A SYSTEM OF
LINEAR EQUATIONS IN TWO VARIABLES
BY THE ELIMINATION METHOD.
What is Elimination?
 Elimination : Eliminating one variable from a system
of equations by
(1) multiplying one or both equations by a
constant, if necessary, and
(2) adding the resulting equations.
Solving Systems by using Elimination
Multiply, if necessary, one or both equations by a
constant so that the coefficients of one of the
variables differ only in sign.
2. Add the revised equations from Step 1. Combining
like terms will eliminate one variable. Solve for the
remaining variable.
3. Substitute the value obtained in Step 2 into either
of the original equations and solve for the other
variable.
4. Check the solution in each of the original
equations.
1.
Solve
x + y = -1
x–y=9
Solve
x + 2y = -11
3x - 2y = -1
Multiply One Equation
2x – 3y = 6
4x – 5y = 8
Multiply One Equation
7x – 12y = -22
-5x + 8y = 14
No Solution
-4x + 8y = -12
2x – 4y = 7