Question

I need help using the substitution method to solve the system
2x + 5y = 10
-3x + y = 36

Answer 1

Ok in the second equation how would you rewrite it to show as 5y =????

Answer 2

@nelsonjedi would equation 2 be revised as y = 3x + 36 ?

Answer 3

Yes. Now we need to reflect the y values as 5y so we can Substitute that value in the first equation. So take y=3x+36 would equate to 5y=???????

Answer 4

I have:
y = 3x + 36
2x + 5y = 10 sub revised eq. 2 into eq. 1
2(3x + 36) + 5y = 10
6x + 72 + 5y = 10
I'm not sure what comes next; this is where I need help

Answer 5

Hi, here's a link I think will help a bit:
http://www.webmath.com/solver2.html

Answer 6

In substitution you are trying to eliminate one of the unknowns (x or y). So if we take y=3x+36 and equate it to 5y...we would multiply each component by 5 and arrive at

5y=15x+180...Do you see this?

Answer 7

So,
y = 3x + 36
5y = 15x + 180 ?

Answer 8

@Matty13579 thank you :)

Answer 9

Yes..now you have a value for 5y from the 2nd equation plug that value into the first equation (substitute) and you can solve for x.

Answer 10

2x + 5y = 10
2x + 5(15x + 180) = 10
2x + 72 + 900 = 10
74x = 10 + 900 (I'm not sure if this is what I'm supposed to do here)

Answer 11

5y =15x+180 so you do not have to multiply it by 5.
When you substitute you will have
2x+15x+180=10
Then combine terms to get 17x+180=10.

Then subtract 180 from both sides and you get 17x= -170...so what does x equal?

Answer 12

17x = -170
x = -10

Answer 13

Now that you know x you can solve for the value of y by plugging it into either of the equations

Answer 14

y = 3(-10) + 36
y = -30 + 36
y = 6

Answer 15

@Mirandaregina You're welcome!

Answer 16

@nelsonjedi thank you very much for helping me out with this :)

Answer 17

Miranda...the only thing you did wrong with your problem is that you subbed in 3x + 36 in for the x value and not the y value.

Your problem should have been set up like this :
y = 3x + 36

2x + 5y = 10
2x + 5(3x + 36) = 10
and just solve for x from here

Answer 18

@texaschic101 ah ok, that's very helpful to know. thank you!