Asked by Cassie

Solve using two different methods. Explain which method you found to be most efficient.

A.
3x - 9y = 3
6x - 3y = -24

B.
7x - 3y = 20
5x + 3y = 16

C.
y = 1/2x - 6
2x + 6y = 19

I am just stuck and don't know how to do these last few problems on my assignment. If someone would please help it would be very much appreciated. Thank You.
Answered by Kuai
A. Elimination method
-6x +18y = -6
6x -3y = -24

15y = -30
y = -2
x = -5

(-5,-2)

B. Elimination method
7x -3y = 20
5x +3y = 16

12x = 36
x = 3
y = 1/3
(3, 1/3)

C . Substitution method
y =x/2 -6
2x + 6y = 19
2x + 6 (x/2 -6) = 19
2x + 3x -36 = 19
5x -36 = 19
5x = 55
x = 11
y = -1/2
(11, -1/2)
Answered by Cassie
Thank you so much. But I need 2 ways to solve each one, can you show me another method for each.
Answered by Damon
I will give you the substitution method for b. Then you do a and c

B. substitution method
7x -3y = 20
7 x = 3 y + 20
x = (3/7)y + 20/7
then
5x +3y = 16
5[ (3/7)y + 20/7 ] + 3 y = 16
(15/7)y + 100/7 + 21/7 y = 112/7
36 y = 12
y = 1/3
go back and get x
Answered by Cassie
Ok. Thank you.
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