# Solving equations graphically.

• Oct 30th 2012, 01:23 PM
Accurate
Solving equations graphically.
Before I start, if this is the wrong section, I'm sorry, I don't really know which section to post it on.

How do I solve these equations graphically :

x+2y=7
x+y=3

This is how I work it out, but for some reason I'm not getting the correct answer, even though I've used it to solve other equations like this :

x+2y=7
Let x=0
0+2y=7
2y=7
y=3.5
Co-ordinate points=(0,3.5)

x+2y=7
Let y=0
x+2(0)=7
x=7
Co-ordinate points=(7,0)

x+y=3
Let x=0
0+y=3
y=3
Co-ordinate points=(0,3)

x+y=3
Let y=0
x+0=3
x=3
Co-ordinate points=(3,0)

So, as we can see, the points for the first equation the co-ordinate points I plot are (0,3.5) and (7,0) and for the second equation I plot (0,3) and (3,0).

The problem I'm having is when I plot them on the graph, they don't intersect, which means I don't have an answer. If they don't intersect, it must be wrong, but how, I think I've done everything correctly? Also, I've looked at other examples in my maths textbook and they work, but for some reason this one doesn't.

• Oct 30th 2012, 04:19 PM
BobP
Re: Solving equations graphically.
They do intersect, just not in the first quadrant.
• Oct 30th 2012, 04:26 PM
skeeter
Re: Solving equations graphically.
Quote:

How do I solve these equations graphically :

x+2y=7
x+y=3
$x+2y = 7$

change to slope-intercept form ...

$2y = -x + 7$

$y = -\frac{x}{2} + \frac{7}{2}$

$x+y = 3$

change to slope-intercept form ...

$y = -x+3$

graph them ...