Question

4x+5y=-18
x=1-4y
use the substitution method to solve.
Can someone please give me a walk through to solve this?

Answer 1

Didn't I answer this a few minutes ago?

Answer 2

No lol....if you did it didnt show up on my page

Answer 3

No prob. In "Substitution" you get one variable all by itself and then you have x = (stuff) or y = (stuff). You then take that (stuff) and put it into the other equation wherever you see x or y.

Answer 4

I got 4(1-4y)+5y=-18
4-16y+5y=-18
-5 -5
4-21y=-18 and from here I am lost?

Answer 5

can you help me finish this?

Answer 6

You're right so far...

4 - 21y = -18

Now add 4 to both sides.

Answer 7

OOOHHHHHH I got 16y+5=14 ??

Answer 8

21y=-14 ?

Answer 9

Wait, no sorry. :(

4-16y+5y=-18
4 - 11y = -18 (negative 16 PLUS 5 = negative 11)

Now subtract four to both sides.

-11y = -22

Answer 10

is y= -0.5?

Answer 11

nevermind I think y=2 ?

Answer 12

Yup. y = 2.
Now just go back to the 2nd equation and subsitute y = 2 to find out what x is. :)

Answer 13

kk...does x=4?

Answer 14

How'd you get that?

Answer 15

i had x=1-4y
so I take x=1-4(2)
and get x=2-8
divide and get 4 ?

Answer 16

Ah, ok. Unfortunately, that is not correct.
FORTUNATELY, the answer is WAY EASIER than you've done. :D

x = 1-4y. That's correct.

x = 1-4(2) (x = one minus four times two) That's correct.
x = 1 - 8
x = -7

Ta-daa! :D

Answer 17

or negative 4

Answer 18

OOH so I don't mu;ltiply the one by 2? I see. Thanks :)

Answer 19

Yup yup!
You can check the graph of it by going to http://www.wolframalpha.com

and typing

plot 4x+5y=-18, x=1-4y