Question

What is the solution of the system?

5x - y = -7
3x - y = -2

A) (-2.5, -5.5)
B) (-2.5, 11)
C) (5, 2.5)
D) (2.5, 5.5)

4x +3y = 12
7x + 5y = 26

A) (18, 20)
B) (18,-20)
C) (-20, 18)
D) (20,18)

Answer 1

5(-2.5)-(-5.5)=-7
3(-2.5)-(-5.5)=-2

4(18)+3(20)=12
7(18)+5(-20)=26

Answer 2

5x - y = -7
3x - y = -2.....multiply by -1
--------------
5x - y = -7
-3x + y = 2 (result of multiplying by -1)
------------add
2x = - 5
x = -5/2 or - 2.5

5x - y = -7
5(-2.5) - y = -7
-12.5 - y = -7
-12.5 + 7 = y
- 5.5 = y

solution is (-2.5 , -5.5)
====================
4x + 3y = 12.....multiply by 5
7x + 5y = 26....multiply by -3
---------------
20x + 15y = 60 (result of multiplying by 5)
-21x - 15y = - 78 (result of multiplying by -3)
---------------------add
-x = - 18
x = 18

4x + 3y = 12
4(18) + 3y = 12
72 + 3y = 12
3y = 12 - 72
3y = - 60
y = -60/3
y = -20

solution is (18,-20)