# simultaneous equation using elimination method

• Jun 1st 2009, 06:07 PM
johnsy123
simultaneous equation using elimination method
can you please solve this equatiion using elmination method.

$\displaystyle 3x+2y=27$
$\displaystyle x-2y=-27$
• Jun 1st 2009, 06:24 PM
artvandalay11
Quote:

Originally Posted by johnsy123
can you please solve this equatiion using elmination method.

$\displaystyle 3x+2y=27$
$\displaystyle x-2y=-27$

Okay, so by the elimination method we just add the equations together. This always works because if A=B and C=D, then A+C=B+C because we are allowed to add the same thing to both sides...

But now we can say A+C=B+D because C=D, so looking back to our original equations we can see that we just added the left side of the first equation to the left of the second and the right of the first to the right of the second....

Onto this question, $\displaystyle 3x+2y+x-2y=27-27$ the left side is 4x and the right is 0 so
$\displaystyle 4x=0$ divide by 4 to get x=0

Now plug x=0 into one of the given equations, I'll use the first one: $\displaystyle 3(0)+2y=27$ so 2y=27 so y= $\displaystyle \frac{27}{2}$
• Jun 2nd 2009, 08:35 PM
Prove It
Quote:

Originally Posted by johnsy123
can you please solve this equatiion using elmination method.

$\displaystyle 3x+2y=27$
$\displaystyle x-2y=-27$

Just a couple of points to remember as well:

You can only eliminate terms if they have coefficients that are the same size.

In this case, you can recognise that the y-values both have coefficients of "size" 2.

Then you check their signs.

If they're the same sign, then you would have to subtract one equation from the other. If they are different sign, then you add them together.

In this case, you can see that one is positive, one is negative, so you would have to add the equations together, as artvandalay said.

Chookas for the exam (Rock)