1. 9P9: Solve 2X2 systems by substitution

2. Find the solution by substitution
Steps
1 Solve 1 of equations for x or y
2 Substitute into other equation
3 Solve for other variable
4 Use answer to find original variable
5 Write answer as ordered pair
6 Check

3. Ex1:Solve by Substitution
x + y = 6 and x = y + 2
1) Done (eqn 2 solved for x)
2) Substitute
3) Solve
4) Find x: x = y so x = or x =4
5) Write solution (4,2)
6) Check =6 yes and 4 = 2 +2 yes
(y+2)+y =6
2y +2 =6
2y=4
y=2

4. Example 2: 4x-y =5 and 2x +y =10
1) Which letter is easiest to solve for? y
4x - y =5 and 2x +y =10
y = x
2) Substitute 4x-(10-2x)=5
3) Solve x-10 +2x = 5
6x -10 = 5
6x=15
4) Find y: so y = y=5
5) ( 5/2,5) is the solution

5. Problem Solving Translate to a system then solve
The sum of two numbers is 82. One number is 12 more
than the other
N1: x
N2: y
x + y = and y = x S1) #2 already solved for y
S2) x +(x+12) =82
S3) 2x +12 = 82
2x =70
x =35
S4) =y
47 =y
S5) The numbers are 35 and 47

6. Assignment
8-2/ /11-29 o, 36-46e,47