Join the growing community of curious minds on IDNLearn.com. Get prompt and accurate answers to your questions from our experts who are always ready to help.

Solving liner systems using elimination?


I need to solve this:

2x + y = -5
3x + 5y = 3


I keep trying, but I can't seem to eliminate and get the correct answer. Thank you so much. :)


Sagot :

y = 3
x = -4

(2x + y = -5)3  =  6x + 3y = -15   = 6x + 3y = -15
(3x + 5y = 3)2  = -(6x + 10y = 6) = -6x - 10y = -6
                                                    -7y = -21    :  y = 3
(then we substitute y into equation #1)
2x + 3 = -5
2x = -8
x = -4

2x + y = -5 .........(i)   
3x + 5y = 3.........(ii)

Now which do you want us to eliminate first, x or y? I hear you saying y. So we are going to eliminate y first.

But if we look at equations (ii) we see that y has 5y, so we multiply equation (i) by 5, so that it has 5y also.


2x + y = -5 .........(i)     (x5).
3x + 5y = 3.........(ii)


5*(2x + y) = 5*(-5) 
10x + 5y = -25.............(iii).

The new equation becomes (iii), and we can now compare (ii) and (iii)

3x + 5y = 3.........(ii)
10x + 5y = -25.............(iii)

Since we have now made 5y on both equations, we can eliminate the y, by subtracting.

Equation  (ii)  Minus (iii).
We perform subtraction before the equality sign and after the equality sign, like in normal subtraction. The xs would subtract the xs and the ys would subtract the ys.

(3x-10x) + (5y -5y) = 3 - (-25)
-7x        +  0y         = 3 +25 .    Minus Minus  is Plus.
-7x                        = 28.    Divide both sides by 7.
x = 28/(-7)
x = -4.

Now we have gotten x, so we can now substitute x = -4, in either equations (i) or (ii). Let us use (i).

2x + y = -5 .........(i)      x = -4.
2(-4) + y = -5.
-8 + y = -5.
y       = -5 +8. (When -8 crossed the equality sign to other side, sign changed)
y      = 8-5
y =3.

Therefore x = - 4, y =3.  That's it. Cheers.
Thank you for contributing to our discussion. Don't forget to check back for new answers. Keep asking, answering, and sharing useful information. IDNLearn.com is committed to providing accurate answers. Thanks for stopping by, and see you next time for more solutions.