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Mr. Sims
Solve using any method.
1. 4x + 7y = -10
3x – 7y = - 4
7x = -14
x = -2
Algebra 2
Section 10.2 E
Substitution or Addition
addition method
add the 2 equations
substitute into any
equation with x and y
4x + 7y = -10
4(-2) + 7y = -10
-8 + 7y = -10
+8
+8
7y = -2
2
y
7
Mr. Sims
2.
6x + y = 0
-6x
-6x
y = -6x
substitute into other
equation for y
15x + 2y = 9
substitution method
get top equation to read y =
15x + 2(-6x) = 9
15x – 12x = 9
3x = 9
into equation
x = 3 substitute
that reads y =
y = -6x
y = -6(3)
y = -18
Mr. Sims
3. -2 3x – 8y = 1
-6x + 16y = -2
6x + 2y = 11
addition method
multiply top by –2
{could also multiply bottom by 4}
6x + 2y = 11
18y = 9
1
y
2
substitute into any
equation with x and y
6x + 2y = 11
1
6x  2   11
 2
6x + 1 = 11
-1
-1
6x = 10
10 5
x

6 3
Mr. Sims
4.
2x + 8y = 8
4 3x – 2y = -16
addition method
multiply bottom by 4
2x + 8y = 8
12x – 8y = -64
14x = -56
x=-4
substitute into any
equation with x and y
2x + 8y = 8
2(-4) + 8y = 8
-8 + 8y = 8
+8
+8
8y = 16
y=2
Mr. Sims
5.
3x – 9y = 3
x + 8y = 9
x = -8y + 9
-8y -8y
substitution method
get bottom equation
to read x =
substitute into other
equation for x
3(-8y + 9) – 9y = 3
-24y + 27 – 9y = 3
-33y + 27 = 3 combine like terms
-27 -27
-33y = -24
x = -8y + 9
8
x  8   9
 11 
64
x   9
11
64 99 35
x 

11 11 11
24
33
8
y
11
y
substitute into equation
that reads x =
Mr. Sims
Algebra 2
Section 10.2 E
Assignment
Use any method to solve the system of equations.
1.) 3x + 4y = 0
9x – 4y = 0
2.) 2x – 5y = 4
3x + 4y = 9
3.) 3x – 4y = 6
4x + 7y = 1
4.) -2x + 3y = 8
x – 5y = - 4
5.) -5x + 2y = 17
3x + 2y = 8
6.) 3x – 9y = 3
x + 8y = 9
Mr. Sims
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Mr. Sims