Question

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.

Answer 1

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)

Answer 2

Thank you so much. But I need 2 ways to solve each one, can you show me another method for each.

Answer 3

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

Answer 4

Ok. Thank you.