# Graph the linear equation and plot intercepts

-4=8x+y

Do you recognise the form: ?
theo.cushion
27 April 2012
yes
bh104
27 April 2012
its for a straight line
bh104
27 April 2012
Can you rearrange into that form?
theo.cushion
27 April 2012
y=8x+-4?
bh104
27 April 2012
Not quite, be careful with the signs
theo.cushion
27 April 2012
Have another go
theo.cushion
27 April 2012
What I wrote it like this:
theo.cushion
27 April 2012
then*
bh104
27 April 2012
Which term do you need to move to the right?
theo.cushion
27 April 2012
the would you divide?
bh104
27 April 2012
Remember we are trying to make look like
theo.cushion
27 April 2012
8x
bh104
27 April 2012
Yes, we need to from both sides. What do you think it will look like then?
theo.cushion
27 April 2012
y+8x-8x=-4 -8x ?
bh104
27 April 2012
Yes, which simplifies to what?
theo.cushion
27 April 2012
-12?
bh104
27 April 2012
Okay we have . What terms do you think will cancel each other out?
theo.cushion
27 April 2012
8x
bh104
27 April 2012
-8x
bh104
27 April 2012
Brilliant, so can you now simplify:
theo.cushion
27 April 2012
You need 2 terms to cancel. So far we have , what will cancel that?
theo.cushion
27 April 2012
would you divide -4 from -8x ?
bh104
27 April 2012
We can do this entirely with addition and subtraction. We know that and cancel, so what do we do with those terms in:
theo.cushion
27 April 2012
subtract?
bh104
27 April 2012
Write out the whole equation
theo.cushion
27 April 2012
I think you've got it
theo.cushion
27 April 2012
y=-8x-(-4) ?
bh104
27 April 2012
Almost!
theo.cushion
27 April 2012
theo.cushion
27 April 2012
which is the same as
theo.cushion
27 April 2012
theo.cushion
27 April 2012
Rearranging can be hard at first, but I think another time we need to go through the rules. Once you're familiar with those it will be much easier.
theo.cushion
27 April 2012
Do you know what the "intercepts" are?
theo.cushion
27 April 2012
x and y coordinates
bh104
27 April 2012
x and y coordinates could be anything, Where would we find the intercepts on a graph?
theo.cushion
27 April 2012
wouldn't you replace the values of x and y
bh104
27 April 2012
like y=-4-8(0) then simplify y=-4
bh104
27 April 2012
Yes!
theo.cushion
27 April 2012
so wouldn't y intercept at -4
bh104
27 April 2012
Exactly, we also know that in the form that C will always be the intercept
theo.cushion
27 April 2012
Okay, what about the x intercept?
theo.cushion
27 April 2012
Remember the original form
theo.cushion
27 April 2012
8
bh104
27 April 2012
Try and break it down into stages
theo.cushion
27 April 2012
theo.cushion
27 April 2012
how do we rearrange that to find ?
theo.cushion
27 April 2012
y=x/8?
bh104
27 April 2012
We are looking at the equation . I have replace with so we can find the x intercept. Just like when you set to in the last bit.
theo.cushion
27 April 2012
We need to get it so that is on his own. At the moment there is an there. How can we move the to the left side?
theo.cushion
27 April 2012
from both sides?
bh104
27 April 2012
0/-4?
bh104
27 April 2012
8 is a little different from earlier as it multiplying
theo.cushion
27 April 2012
subtract
bh104
27 April 2012
Okay think of it a different way.
theo.cushion
27 April 2012
We could divide both sides by 8
theo.cushion
27 April 2012
to give
theo.cushion
27 April 2012
theo.cushion
27 April 2012
8x/8x cancel out
bh104
27 April 2012
Yes,
theo.cushion
27 April 2012
so what is the value of the x intercept?
theo.cushion
27 April 2012
, or more simply
theo.cushion
27 April 2012
So we could write , or more simply
theo.cushion
27 April 2012
Sorry
theo.cushion
27 April 2012
4
bh104
27 April 2012
1
bh104
27 April 2012
Not quite, if we make it look like this, it might be clearer
theo.cushion
27 April 2012
would you divide -4/8 ?
bh104
27 April 2012
We could also say it in words. x equals minus 4 divided by 8.
theo.cushion
27 April 2012
So lets recap
theo.cushion
27 April 2012
Yes
theo.cushion
27 April 2012
-0.5.
bh104
27 April 2012
so what value is minus 4 divided by 8?
theo.cushion
27 April 2012
the intercept is , and the intercept is
theo.cushion
27 April 2012
Are you comfortable drawing that?
theo.cushion
27 April 2012
not really i never graphed -0.5 or other like it, how would you?
bh104
27 April 2012
Have you got some squared paper?
theo.cushion
27 April 2012
yes
bh104
27 April 2012
Draw a set of axes in the middle of the page. What range should you put on the axes to make sure we get both of the intercepts in?
theo.cushion
27 April 2012
bh104, I must go now. You can see an example of the graph here: http://bit.ly/I8kcFE . Look at the X and Y axes and see where the lines crosses them.
theo.cushion
27 April 2012
point o -4
bh104
27 April 2012
ok thank you
bh104
27 April 2012
My pleasure. Hope it helped
theo.cushion
27 April 2012
Yes thank you
bh104
27 April 2012
If you have any more questions then post them up
theo.cushion
27 April 2012