# Thread: Solving simultaneous equations using the substitution method.

1. ## Solving simultaneous equations using the substitution method.

Thanks,
That did help a lot. I tried doing one on my own right after, but am a little stuck.

x-2y=4
2x-4y=5

I did:

2y=4+x
2x-4(4+x)=5

2x-16+4x=5 ----> 6x = ?

2. ## Re: Solving Using Substitution

Edit: Your method is littered with small errors: did you check it?

$1) x-2y=4$

$2) 2x-4y=5$

From $1)$, $x=4+2y$

Substituting this into $2)$:

$2(4+2y)-4y=5$

Try to solve this, and you will realize that $8\neq{5}$ as the original equations suggest. Do you have a typo?

3. ## Re: Solving Using Substitution

Originally Posted by annon25
Thanks,
That did help a lot. I tried doing one on my own right after, but am a little stuck.

x-2y=4
2x-4y=5

I did:

2y=4+x
2x-4(4+x)=5

2x-16+4x=5 ----> 6x = ?

Did you make up these two equations? As Quacky proved, 8 does not equal 5. Here are two more samples for you to practice.

2x – 3y = –2
4x + y = 24

AND the second below

7x + 2y = 16
–21x – 6y = 24