Can you show me how to solve this equation using substitution
5y+4x=8
y=5x+10

- anonymous

Can you show me how to solve this equation using substitution
5y+4x=8
y=5x+10

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- amistre64

yes. since it is stated that y = 5x +10; we can just substitute that value for "y" in the other equation and slove for "x"

- amistre64

5(5x + 10) + 4x = 8
25x + 50 + 4x = 8
29x + 50 = 8
29x = 8 - 50
29x = -42
x = -42/29

- amistre64

reduce if you can...

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## More answers

- anonymous

could you show me what I did wrong ill show you how I solved it

- amistre64

go right ahead :)

- anonymous

5y+4x=8
y=5x+10
5(5x+10)+4x=8
25x+50+4x=8
21x+50=8
21x=-42
x=-2
y=5(-20)+10
y=-10+10
y=0

- anonymous

That is what I did

- anonymous

And I was pretty sure that was the answer.

- amistre64

25x + 4x does NOT equal 21x

- anonymous

Oh sorry I made a typing misatke to y=5(-2)+10 should be the one line

- anonymous

Ithought you subtracted

- amistre64

nope; when it says 25 + 4, it actually means to add. That little (+) sign means add....

- anonymous

I know but I was taught that you did the opposite to get rid of it

- amistre64

why would you want to get rid of it? it is a vital part of the equation. Now, if it was on the OTHER side of the (=) sign, you would subtract it from BOTH sides to move it.
But, if it is on the SAME side, it is simply addition....
Does that make sense?

- anonymous

Look at your original question that you asked. Are you sure it doesn't say -4x in the problem you were given? 5y - 4x = 8?

- anonymous

Hold on let me check quick

- amistre64

If you want to move it to the othe side of the (=) sign we do this:
25 + 4 = 29
25 + 4 (-4) = 29 (-4)
25 = 29 - 4
But when it is on the same side, just add it together:
25 + 4 = 29
29 = 29

- anonymous

5y + 4x = 8
y + 5x = 10
it says ''solving a system of equations by substitution''

- amistre64

That is a different set of equations that what you give to begin with; please verify which one is correct please...

- anonymous

Im sorry

- anonymous

The last one is the correct one

- amistre64

ok :)
What does "y" equal then?:
y = 10 - 5x
substitute that "value" into the top equation to get:
5(10 - 5x) + 4x = 8
50 - 25x + 4x = 8
-25x + 4x = 8 -50
-21x = -42
x = -42/-21 = 2
Use this solid value of x=2 in the bottom equation to solve for "y"
y + 5(2) = 10
y + 10 = 10
y = 10 - 10
y = 0
x = 2

- anonymous

OK thanks im gonna look over this for a minute

- anonymous

Im sorry im kinda confussed I was taught in a different way and im trying to figure this all out

- anonymous

I got y=5x+10

- amistre64

you gave, for the bottom equation:
y + 5x = 10 ; to get "y" all by its little lonesome, we need to subtract (5x) from both sides to keep the same values...
y +5x -5x = 10 - 5x
y + 0 = 10 - 5x
y = 10 - 5x
Do you see it?

- anonymous

Not really im sorry

- amistre64

tell me where I am losing you then, let me know what is confusing you here. And then I can show you the right steps...

- amistre64

Can you tell me what the (=) sign means?

- anonymous

See for Y im somehow got -5x+10

- amistre64

-5x + 10 is correct, and it is the same thing as 10-5x
am i right or wrong?

- anonymous

Oh so then I did have it right?

- amistre64

you wrote, and I quote " I got y=5x+10" earlier.
If what you meant was "I got y= -5x+10" then yes, you are right...

- anonymous

Yeah thats what I meant im sorry I cant type today at all

- amistre64

:) paper and pencil is always easier when doing math

- anonymous

Yeah it is but thanks for showing me that now im gonna rework the problem and see if i get it right

- anonymous

so should the set up be 5(-5x+10)+4x=8

- amistre64

Yes

- anonymous

Ok I think im getting this down now

- amistre64

you are doing great :)

- anonymous

Thanks I have really been having a tough time this year

- anonymous

Does y = 2

- anonymous

and x=0

- amistre64

yes; y=0 and x=2.
To double check; plug those values into the original equations to see if they are true.

- anonymous

Ok thanks a lot :)

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