Confused with Substitution.

Levie:

I've been struggling with substitution in math, to specify, Algebra I substitution, my teachers way of explaining it never really stuck in my head, I've been confused about it ever since and that there's a quiz coming up and I really want to do good on it, please help me understand better.

Have a look at this page - It might help. Come back and tell me how you got on.

http://www.mathsisfun.com/algebra/substitution.html

it didn't help that much

Levie:

it didn't help that much

I'm assuming that you're asked to use substitution on for example two equations,

eg.

1) 2x+2y = 4
2) 5x+y = 6

Now, if we want to substitute then 'pretend' y is already a number and we want to know x in equation number 1).
Then we have 2x + 2y = 4 => 2x = 4-2y => x = 2-y

Now in equation 2), we 'substitute' x with 2-y for every x in equation 2) (because we just saw x = 2-y)

Then we have 5x+y = 6 => 5*(2-y) + y = 6 => 10-5y + y = 6 => 10-4y = 6 => -4y = -4 => y = 1.

Now that we know y = 1, we can calculate x be filling y in in either of the equations.

for equation 1) ; 2x+2y = 4 => 2x + 2*1 = 4 => 2x + 2 = 4 => 2x = 2 => x = 1

and to check i'll show the same thing for equation 2);

5x + y = 6 => 5x + 1 = 6 => 5x = 5 => x = 1

As you can see the answer is y = 1, and x = 1.

Simple said, we solve the first equation for one of the variables and then 'fill in' or 'substitute' that variable in equation 2.

Hope this helped.

I guess for us to help you we probably need to understand your problem better.

For example

1) If y=x+8 and x=5
can you tell me what y will be?

if you can do this one easily, perhaps you could tell us one that you don't quite understand.
We really do want to help you.

Melody:

I guess for us to help you we probably need to understand your problem better.

For example

1) If y=x+8 and x=5
can you tell me what y will be?

if you can do this one easily, perhaps you could tell us one that you don't quite understand.
We really do want to help you.

More like Reinout's explanation, his made things a little clearer

Levie:

Melody:

I guess for us to help you we probably need to understand your problem better.

For example

1) If y=x+8 and x=5
can you tell me what y will be?

if you can do this one easily, perhaps you could tell us one that you don't quite understand.
We really do want to help you.

More like Reinout's explanation, his made things a little clearer

I am glad that reinout was able to help you.
Reinout has used substitution to solve two equations simultaneoulsy.
If his two equations were plotted on a number plane, they would both be lines.
His solution (1,1) would be where the 2 lines cross. That is, where the two equations are simultaneously true.