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in desperate need of algebra help

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Deleted member 17990

Banned
Oct 27, 2017
7,461
just gotten to simultaneous equations and it doesn't make any sense at all to what to do

if anyone can help that would be great

y = 2x + 3 and y = 5x - 12

this question is apparently one of the easier ones and I've been shown the steps but doing the steps is whats confusing me the most
 
ChrisR

ChrisR

Member
Oct 26, 2017
6,797
Substitute one value for the other

y = 2x + 3
y = 5x - 12

2x + 3 = 5x - 12
2x + 15 = 5x
15 = 3x
x = 5

y = 2 * 5 + 3
y = 13
 
Shwing

Shwing

Member
Oct 25, 2017
858
Since 2x + 3 and 5x - 12 are both equal to y than they are both equal to each other.
 
jariw

jariw

Member
Oct 27, 2017
4,283
Since...

y = 2x + 3 and y = 5x - 12

...and you know that the following is always true:

y=y

...so...
one of the y = the other y

...which means that...

2x + 3 = 5x - 12
 
subpar spatula

subpar spatula

Refuses to Wash his Ass
Member
Oct 26, 2017
22,129
Y=2x+3

2x+3=y

2x+3-3=y+-3

2x=y-3

2x/2=y-3/2

X=1 over 2y + -3 over 2.

That is my brain trying to remember algebra.

Oh shit I didn't see the simultaneous part. Me dumb.
 
Sandfox

Sandfox

Member
Oct 25, 2017
24,743
Russell said:
yes but when you move the -12 to the plus 3 why does it become addition instead of negative
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Click to shrink...
You're adding 12 to the right side to remove it and then you have to do the same to the other side.

Basically the rule it "what you do to one side of the equation you must do to the other"
 
RiOrius

RiOrius

Member
Oct 27, 2017
6,081
Russell said:
this is the problem I am having,

none of this makes sense to me I don't know where to start with it.
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So, y = y, right? And you've already got:

y = 2x + 3 and y = 5x - 12

So you can plug one of the things that y equals in for the other. Now you've got

2x + 3 = 5x - 12

That's just a normal equation with one variable. Solve it for x:

15 = 3x
x = 5

Now you need to find y? Well, you've got two different equations for y, and now you know x. Plug your value for x into either one, you'll get y:

y = 2x + 3 = 2(5) + 3 = 13
y = 5x - 12 = 5(5) - 12 = 13
 
AIan

AIan

Member
Oct 20, 2019
4,866
Just don't think of "x" and "y" as foreign letters to some mysterious alphabet. Think of them as "mystery numbers" and your goal is to isolate these letters (numbers) so that it equals to the answer. You're trying to find x—one mystery number—in order to figure out the y number.

While I've been calling "x" and "y" letters, they're called variables mathematically.

Excuse if I came across as maybe ignorant or redundant, I have no clue how far you are in algebra.
 
BarryFishFinger

BarryFishFinger

Member
Oct 27, 2017
7,484
Russell said:
yes but when you move the -12 to the plus 3 why does it become addition instead of negative
Click to expand...
Click to shrink...

It's just one of the rules. If you move something to the other side of the = sign then you flip whether it's postive or negative. So a -12 on one side, move to the other side becomes a +12 which you can then add to the +3 for a total of 15.

Basically you want to try and sort the numbers together and the symbols together.
 
Unknownlight

Unknownlight

One Winged Slayer
Member
Nov 2, 2017
10,570
Let's actually start with the basics here. When you have a pair of questions like that, are you aware that the x in one question is intended to be identical to the x in the other question? If one x is 4, then the other x is 4 too.
 
RagnarokX

RagnarokX

Member
Oct 26, 2017
15,782
Russell said:
this is the problem I am having,

none of this makes sense to me I don't know where to start with it.
Click to expand...
Click to shrink...
Since y = both 2x + 3 AND 5x - 12 both of those equations equal each other. (2x + 3) IS y. (5x - 12) IS y. So in y = 5x - 12 you can put the other equation for y where the y is, giving you 2x + 3 = 5x - 12.

Anything you do to 1 side of an equation has to be done to the other.

So you add 12 to get rid of the - 12 on one side and also add 12 to the other side to get 15.
2x + 3 + 12 = 5x - 12 + 12
2x + 15 = 5x + 0
2x + 15 = 5x

Then you want to get the x's to one side by subtracting 2x from both sides.
2x - 2x + 15 = 5x - 2x
0 + 15 = 3x
15 = 3x

Then you get rid of the x multiplier by dividing both sides by 3.
15/3 = 3x/3
5 = x
 
RiOrius

RiOrius

Member
Oct 27, 2017
6,081
Russell said:
ok what about this one

3y = 8 - 3x and 2y = 3x + 2
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Click to shrink...
Oh man, so I'm gonna warn you up front: the numbers here are gonna be messy. So just a heads-up: you're gonna get fractions, that's not a sign you're doing it wrong, it's just a sucky problem.

So the reason things were easy with the first one was because you already had them both as y = and y =. To do this one, you need to get one of them in that form. Or both if that's your jam, but really one is all you need. So do some algebra magic, like you're solving for x, to isolate y on the left side of the equation.

It sounds like you may not be super comfortable with those operations, but let's see what you've got, and if you mess up we'll help you out.

So yeah, just start there. 3y = 8 - 3x. How would you get that to something that just says y=?
 
GeoGonzo

GeoGonzo

The Fallen
Oct 25, 2017
4,329
Madrid, Spain
Russell said:
i don't know what to do which is the problem
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Starting from the very beginning, do you follow through with these two posts?

Unknownlight said:
Let's actually start with the basics here. When you have a pair of questions like that, are you aware that the x in one question is intended to be identical to the x in the other question? If one x is 4, then the other x is 4 too.
Click to expand...
Click to shrink...

AIan said:
Just don't think of "x" and "y" as foreign letters to some mysterious alphabet. Think of them as "mystery numbers" and your goal is to isolate these letters (numbers) so that it equals to the answer. You're trying to find x—one mystery number—in order to figure out the y number.

While I've been calling "x" and "y" letters, they're called variables mathematically.

Excuse if I came across as maybe ignorant or redundant, I have no clue how far you are in algebra.
Click to expand...
Click to shrink...
 
Heroicpiglet

Heroicpiglet

Avenger
Dec 22, 2017
2,065
The left and the right of the "=" must be perfectly balanced, as all things should be. So when you add/minus/multiply/divide an amount to the left, you must do the same to the right.

1 = 1
1 + 5 = 1 + 5
1 + 5 - 5 = 1 + 5 - 5
 
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