Plotting the intersecting point

• September 11th 2008, 11:48 AM
tobiemc
Plotting the intersecting point
My equation is: x+3y=4 and 2x-y=1 I need to plot the intersecting point on a graph and cannot seem to come up with the correct answer.
• September 11th 2008, 12:02 PM
Jameson
Quote:

Originally Posted by tobiemc
My equation is: x+3y=4 and 2x-y=1 I need to plot the intersecting point on a graph and cannot seem to come up with the correct answer.

If you're graphing these, then it's easier to convert them to the form of y=mx+b.

So x+3y=4 -> y=-x/3+4/3 and 2x-y=1 -> y=2x-1.

Set the two equations equal to each other and graph it. :)
• September 11th 2008, 02:16 PM
tobiemc
It is after that point I am having trouble with...
I have gotten to this point in the equation. My teacher says I have to solve for X and then graph that and that is what I am having trouble with.
• September 11th 2008, 02:53 PM
Jameson
It's not as usual to solve for x and graph it but what's the problem? Is the algebra tripping you up?
• September 11th 2008, 03:20 PM
tobiemc
I can't graph 4/3, it has to be a whole number so my teacher told me to solve for x instead. When I try to solve for x my answers come out wrong. Could you show me the problem worked out step by step so I can see where I am messing up.
• September 11th 2008, 04:04 PM
Jameson
Quote:

Originally Posted by tobiemc
My equation is: x+3y=4 and 2x-y=1 I need to plot the intersecting point on a graph and cannot seem to come up with the correct answer.

#1) x+3y=4
x= 4-3y

#2) 2x-y=1
2x=1+y
x=.5y+.5

You have to have a fraction or decimal when solving for x, unless in the second one you solve for y.

y=2x-1
• September 11th 2008, 04:28 PM
tobiemc
I graphed it as -3y on the grid, 4/1 as the slope and then graphed -1 on the grid and 2/1 as the slope. The intersect point was 1,1 but it was wrong. (Headbang)
• September 11th 2008, 04:51 PM
Jameson
Quote:

Originally Posted by tobiemc
I graphed it as -3y on the grid, 4/1 as the slope and then graphed -1 on the grid and 2/1 as the slope. The intersect point was 1,1 but it was wrong. (Headbang)

You are not graphing the first equation correctly. Like I said x= is not the usual form for graphing a linear equation because you don't get the immediate information of the slope and intercept. The y-int is 4/3 and the slope is -1/3.
• September 11th 2008, 05:11 PM
tobiemc
I am still being told that my answer is incorrect even with y-int is 4/3 and the slope is -1/3. I have no idea what I am doing wrong. Thank you so much for all your help though.
• September 11th 2008, 05:15 PM
Jameson
Quote:

Originally Posted by tobiemc
My equation is: x+3y=4 and 2x-y=1 I need to plot the intersecting point on a graph and cannot seem to come up with the correct answer.

Ok so we have y=(4-x)/3 and y=2x-1. Set them equal to find out the intersection point. (4-x)/3=2x-1. 4-x=6x-3 7x=7x. Plug x=1 into either equation and you get y=1. So the point is (1,1)
• September 11th 2008, 06:06 PM
tobiemc
It is the 4/3 that keeps stumping me. I have had no trouble being able to get a correct answer on any of my other problems but all my problems that have a fracture in them I cannot get the answer. I don't know how to plot the 4/3.
• September 11th 2008, 06:08 PM
Jameson
Quote:

Originally Posted by tobiemc
It is the 4/3 that keeps stumping me. I have had no trouble being able to get a correct answer on any of my other problems but all my problems that have a fracture in them I cannot get the answer. I don't know how to plot the 4/3.

Are you drawing these on a computer program or by hand? If by hand, then $\frac{4}{3}$ is one and one-third. I would just try to get as close as possible.
• September 11th 2008, 06:15 PM
tobiemc
It is a computer program.
• September 11th 2008, 06:18 PM
Jameson
I don't know what to tell you. I've double checked my work and I'm pretty sure I have the right answer. Maybe look in a guide online? Or call a friend who might know how to input fractions.
• September 11th 2008, 06:22 PM
tobiemc
Thanks for spending so much time trying to help.