can somebody help me..........?

Question

tomorrow i have a math test, but i don't understand how to do this:
this is a example :
y=3x x+y=12
x+y=12 x+3x=12

4x=12
this is te answer: x=3
then i have to solve for y :
y=3x
y=3(3)
this is the answer: y=9
so the final answer is : (3,9)

i don't get how to do this:
x+2y=13
x=y+4
PLEASE!!!!somebody explain me how to do this

Answer 1

plug in y+4 where X is
so you get y+4+2y=13
which is 3y+4=13
subtract 4 so its 3y=9
y=3
plug in y to get x=3+4
x=7

(7,3)

Answer 2

For the first one:

All you are doing is *substituting* in a variable.

Here's how it works.

You are given:

y = 3x and x + y = 12

First, put "3x" in place of y in "x+y=12". This way, all you have to deal with are "x's" and not "y's".

Make sense?

So you have x + 3x = 12.

Now, combine those x's.

4x = 12

Now divide... x = 3

Okay. Now we know that x = 3. Plug that into y = 3x and you get y = 3(3) = 9. Just like you wrote above.

The answer is (3,9)

For the second problem:

You are given x+2y = 13

x = y+4.

First step: Substitute "y+4" in place of the "x" in x+2y

You'll get:

y+4+2y =13. (Now all you have to deal with are the "y's")

Now combine like terms.

3y + 4 = 13
3y = 9
y = 3

Since you know that y = 3, put that back into x=y+4

x = y+4
x = 3+4
x = 7

So the answer is (7,3)

Hope that helped.

Regards,

Mysstere

Answer 3

If x+2y =13 then it can be said that x = -2y+13
then you have x = -2y+13 and x = y+4 because x = x you can say that:
-2y+13 = y+4
then you get the y's alone on one side...
(13-4) = (y+2y) or 9 = 3y
so then divide by 3
y = 3
Then you plug 3 back into one of the origonal equations:
x = (3)+4
so x= 7
your answer is (7,3)

Hope this helped...
Best of Luck on your test : )

Answer 4

use the substitution method...
x+2y=13 over
x-y=4

subtract then x cancels out and your left with 3y=9 so y=3
then plug it in x+2(3)=13 which equals x+6=13 so x=7
final answer is (7,3)

Answer 5

x + 2y = 13
x - y = 4
------------------ subtract the second equation from the first you get
x-x + 2y -(-y) = 13 - 4
0 + 2y + y = 9
3y = 9
y = 9/3 =3

substitute y
x - (3) = 4
x = 4 + 3 = 7

x = 7, y = 3

Answer 6

first we have to put the variables on one side by themselves. so we will have: x+2y=13
x- y=4
use elimination method to solve for one variable. to do that multiply the second equation by -1 so it becomes
x+2y=13
-x+y=-4
add the two equations so now you have 3y=9 ad y=3
now plug i your value to find x
you can us Any one of them to do that. x-3=4, x=7
or you can use x+2(3)=13
x+6=13
x=7
so your answer is (7,3)
good luck!!!!