I don't understand solving using for the elimination method. Algebra is like chinese to me can some help me... here is an example of a problem...

4x-2y=-2
4x+3y=-12
:mad::mad::mad:
:confused::confused::confused:

Quote:

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4x-2y=-2
4x+3y=-12

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Subtract the second equation from the first



Viola! X is eliminated!



Substitute this back in to either of the equations to solve for x.

If the coefficients of the variable you're going to eliminate aren't the same, multiply the entire equation -- or both equations, with constants so that when added, one of the variables will be "eliminated".

Quote:

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Originally Posted by Perito

Subtract the second equation from the first



Viola! x is eliminated!

Substitute this back in to either of the equations to solve for x.

If the coefficients of the variable you're going to eliminate aren't the same, multiply the entire equation -- or both equations, with constants so that when added, one of the variables will be "eliminated".

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so it's that easy because how do i no to subtract sometimes there are questions like
8x-y=20
5x+y=-8

Quote:

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8x-y=20
5x+y=-8

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multiply 8x-y=20 by 5
multiply 5x+y=-8 by -8

40x -5y = 100
-40x -8y = 64

add them

-13y = 164
y = -164/13 ≈ 12.616

You could also just add them directly since the y-coefficients are the same (in absolute value). This would eliminate y

8x-y=20
5x+y=-8

13x = 12
x = 12/13


You can select constants to multiply each equation with. It'll still be an equation.

Quote:

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Originally Posted by Perito

multiply 8x-y=20 by 5
multiply 5x+y=-8 by -8

40x -5y = 100
-40x -8y = 64

add them

-13y = 164
y = -164/13 ≈ 12.616

You can select constants to multiply each equation with. It'll still be an equation.

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how do I still find x and for the first equation I plugged in x and got 8. is that right? (8,-10)

I made a sign error in my first post. :mad: :rolleyes: Y is -2 in the first problem. X will turn out to be -3/2

Yes, you just plug that into either equation and solve for x. To check it, insert the values for x and y into the other equation and it has to be an equality. That's how I figured out that I had made a mistake.