How in the world do I graph x + y = -5?

Question

Ok, my math book doesn't explain it, and neither does the internet. So, how in the world do I graph x + y = -5 without knowing the x or the y? And what about -3x + y = 6? Thanks for the help. :D

Yeah, I know I'd have to solve the equation. But how do I solve the equation if I don't know x and y?

Answer 1

all you need to do is suppstitue 0 in for the x or y variable... say you wanna find where the line crosses the x-axis... so you put 0 in fo y to get x+0=-5 or x=-5 so put a point at (-5,0). same for the more complicated one... if you want to find y do -3(0)+y=6. so your line would cross the y-axis at 6.. hope this helps

p.s. or you could put it in slope intercept form(y=mx+b) and figure it out that way...

Answer 2

To say "the internet" doesn't explain how to graph a line is absurd! Surely you can find SOME pages on how to do this if you search around. I just scrolled all the way up and entered "How to graph an equation" into the Yahoo.com search box on the top of the page (because Yahoo.com is after all a search engine) and found these right away:
http://www.ehow.com/how_2848_graph-linear-equations.html
http://library.thinkquest.org/20991/alg/CPGraphing.html
http://www-unix.oit.umass.edu/~tduong/linearequation.htm
http://www.wtamu.edu/academic/anns/mps/math/mathlab/int_algebra/int_alg_tut14_lineargr.htm

If x and y had exact values, then it wouldn't be a graph, it would just be a pair of values. You have one equation with two variables, so you'll never get an exact number for each of them, which is not what we're trying to do anyway. The point in making a graph is to show all of the values of x and y that make this equation true. You can't write them all out because there are an infinite number of pairs that will fit, but there are an infinite amount that won't fit either.

Graphs are useful because they show us how one variable changes with the other. They're used by people all the time to look up answers without needing to calculate with the equation, predict future outcomes based on current trends, etc.. Different equations give you different sorts of lines and curves when graphed.

When we say "solve this for y", we mean "write an expression for y in terms of x", because we have a second variable. If you subtract x from both sides, you get y = -x - 5. It turns out that any equation that you can rewrite as y = mx + b (where and b are constants) will always give you a STRAIGHT LINE. There are a couple of different ways of graphing a line. See the links.

Answer 3

Let x = 0 and then complete the equation to find y. So for example:

If x = 0, then y = -5
If x = 1, then y = -6
If x = 2, then y = -7

and so on. Then you plot the coordinates (0,-5), (1,-6), (2,-7) on a graph.

Answer 4

It's a line. y = -x - 5

Pick a value for x and find out what y is
If x = 0, y = -5

Pick another value for x and find out what y is
If x = -5, y = 0

Plot these two points on a graph.
Connect them with a straight line that extends onward past each of these points to infinity in each direction.
Voila! You are done!


Do the same for -3x + y = 6; y = 3x + 6
If x = -2, y=0
If x = 0, y = 6
Plot. Connect. Draw line. Done!

Answer 5

Take a series of x values
e.g. 1, 2, 3, 4, 5

x + y = -5 so y = -5 - x

Now you can calculate the y value for each x value

x y
1 -6
2 -7
3 -8
4 -9
5 -10

Plot these points and, as it's a straight line, join them all up

Answer 6

Equation is x+y=-5
so, x= -y -5
then
If y=1 then x= -1-5= -6
If y= -1 then x= 1-5= -4
If y= -5 then x= 5-5= 0
on graph mark co-ordinate as (-6,1);(-4,-1);(0,-5)
and u will get a graph

Answer 7

put the equation in the correct form: Y=mX + b (it's a line)

y = -x - 5

so when X=0 y = -5 First point of your graph
the slope (change in Y / change in X) of the line is m = -1

next point is X = 1, Y = -6 or just use any X you want

Connect the dots

Answer 8

Dude, just get a TI-83 or better calculator and type the equation in the graph function. Easy as pie.

Answer 9

You have to solve the equation.

Answer 10

I think you have to solve for y, and then graph the y=.