L O.

asked • 12/27/13

how do you solve 4x - y = 5 and 4x + 4y =-4 using elimination

Please solve the linear system using elimination.
 
                             4x - y = 5
                             4x + 4y = -4
 
Please show steps.
 
Thanks

3 Answers By Expert Tutors

By:

Vivian L. answered • 12/27/13

Tutor
3 (1)

Microsoft Word/Excel/Outlook, essay composition, math; I LOVE TO TEACH

Parviz F. answered • 12/27/13

Tutor
4.8 (4)

Mathematics professor at Community Colleges

L O.

I am confused.  If  I put 3 for y then the first equation I get 2 for x.  4(2) - 3 = 5.  But when I use the same for the 2nd equation, it doesn't work.  I get a positive 4 for the answer.
 
-4(2) + 4(3) = 4.   Equation 2's answer is a -4.
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12/27/13

Paul H.

Actually, this one was done in a heap of hurry. The SECOND equation should have been written as
 
-4x -4y = +4
 
Then when you add I and II together, you get -5y = 9  or y = - 9/5
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12/27/13

Parviz F.

You have to Substitute in :4X + 4y = -4 
 
    To get the answer.
 
      The whole 2nd equation was multiplied   by -1 to subtracted from the first equation.
      You used substitution by only multiplying the first term 4X by -1. 
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12/27/13

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