#1
I have to do this bullshit hwk that my teacher gave me so I can pass a stupid little quiz that I will be having tomorrow. I need to pass it because it's a first impression of my second semester. Someone explain to me please:

x - y = 4

x + y = 2

It tells us to solve it by graphing, I at least want an explanation on how to graph it.
thanks in advance.
#2
are you just trying to graph this, or are you trying to fiigure out where the two lines intersect? Once you tell me I can help you
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#3
I'm doing this now. Are you trying to see if its a linear graph or are you trying to solve for the y variable by substituting your own values for the x?

Yeah, like he said^ are u doing the x and y intercepts?
Last edited by guitarguy5515 at Feb 1, 2007,
#5
Are you trying to just get it into slope-intercept form?
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#6
you just set both equations = to Y and then equal to eachother , and the answer is y=3 X=-1, those values will work on both eqautions
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#8
put them both into slope intercept form (y=mx+b)

the first would then be y=x+4

the 4 is your Y axis (count up 4)

then go up 1, over 1 (as this is your slope- 1/1)
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#9
i'm sure we're supposed to find out where the lines intersect. The problem says ''solve each system by graphing''
#11
Solve by graphing implies finding a point of intersection. First you'll want them set equal to Y, so you can graph them. So we have:

x - y = 4
+y +y

x = 4 + y
-4 -4

y=x-4

and the other

x + y = 2
-x -x

y=2-x

now just graph them, plugging in the X and finding the Y to make lines out of them. When you do that for both, you'll find a spot where they intersect. That spot is your solution, and you give the (x,y) coordinate of that intersect.
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#12
Well, if you have to graph... First step would to be get it into y = mx + b form... Then, graph. =)

You would get y = x - 4 and y = -x + 2. Hope that helps.
#13
Then set your y value to 0. solve. Then set your x value to 0. solve. Those are the coordinates for the x and y intercept. graph them.
#14
Quote by hippieboy444
what the hell?


You're 12, not going to be doing this anytime soon.
#15
basically just graph a point like if x=1 then y=-3 for the first and y=1 for the second, just do that and graph each line then find the point where the lines intersect... good luck on the algebra test tommarow bro (we just finished all the stuff with graphing linear equations a few weeks ago lol)
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#16
waste of time to solve by graphing, easier just to solve with subsitution. This stuff is easy. If it's only for an impression why do you care so much. You'll be setting a false impression anyways.
#17
i understood precal ok. but **** i hated it when they give you a bunch of linear equations or just equations in general and say "solve." like wtf is that supposed to mean. but really, it's simple once you start doing homework.
#18
x - y = 4 ===> y = x - 4

x + y = 2 ====> y = 2 - x

therefore x - 4 = 2 - x
2x = 6
x = 3

and if x = 3, x + y = 2, so 3 + y = 2.. so y = -1
OR x - y = 4, so 3 - y = 4, so y = -1

so x = 3, y = -1, solved, without needing to graph it
#19
Quote by iheartgruffruff
lol aww little kid math this is qute some1 help him

Haha I know.....I looked at this and nearly laughed. I remember doing this stuff 4 years ago.
..............
#22
okie dokie.... firstly, rearrange:

y=-x+2

y=x-4

the +2 and the -4 is where the xy intercepts are. so, for y = -x+2, that line will cross at y=2 (0,2). y=x-4, the line will cross at y=-4 (0,-4). Plot the graph, and find the point of intersect. To save time, I've worked it out for you. The point of intersect is (3,-1).

y=x-4 runs through: (0,-4) (1,-3) (2,-2) (3,-1) (4,0) (5,1)

y=-x+2 runs through (0,2) (1,1) (2,0) (3,-1) (4,-2)

Good luck, if you see this before your test
#23
I wish my math class was still like that...
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#24
Now they're like, "Differentiate the function f(x)dx and use the 2nd Fundamental Theorem of Calculus to solve secx blah blah blah."

I miss Algebra II!
#25
Quote by MuffinMan
I wish my math class was still like that...


I've just come out the other end of A-Level Maths only last year.... and biomedical sciences has only got me doing an extra module of statistics

Dammit.... I hated doing long division of quadratic equations involving sin, cos, tan, sec, cosec, cot etc..... DAMN INVERSE TRIGONOMERTY

and even though the non graphed answers are correct, it's usually best to answer a question as it asks you to.... more likely to get the full marks. And it's not the answer that's important, it's the knowledge that you can use that particular method to reach the answer.
#26
Quote by toha33
oh ok thx so much guys. I got it:

y=-1+4=3
y=2(-1)=-1



no when they say SOLVE, it means find what x equals and find what y equals.
When you say that y = 3, then it cant = -1.

the answer is X = 3, and Y = -1.

If you put it like this (x, y)

then the answer is (3, -1).