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# Coordinate geometry watch

1. (Original post by strangepath)
I am such an idiot, the answer was written right there
Hi, sorry for the late reply, was busy revising maths myself too. Anyway for Q4 what you need to do is get the equation in the form y = mx + c so y shouldn't have any co-efficient in front of it, from there you can just read the gradient off. Since it is perpendicular put the gradient in the form -1/m. It says the line passes through the origin so then you can just put it into the straight line equation!

For Q6, you're finding the equation of the perpendicular bisector, so find the normal gradient of AB, then put that gradient in the form -1/m, that's your gradient. Since it 'bisects' the other line, the point you use in the straight line equation will be the midpoint of AB, put the info into the straight line equation and there's your answer.
2. (Original post by strangepath)
I find the last 2 pics really difficult but I would be really glad if you could help me with the rest of the questions.
I have a rough idea about the last one, you can find the gradient of the line which is 2000/1000 = 2, and if you extrapolate that line it intersects the y axis at about (0, 25), I'm not confident about this one though so don't just take my word for it. For the next one, since the lines linear, it'll go in equal steps so couldn't 4000 minutes be $65, since 1000 is$35, 2000 is $45, 3000 could be$55 and 4000, 65? Like I said though, this is a q I'm not too confident with so check to make sure.
3. (Original post by Magenta96)
I have a rough idea about the last one, you can find the gradient of the line which is 2000/1000 = 2, and if you extrapolate that line it intersects the y axis at about (0, 25), I'm not confident about this one though so don't just take my word for it. For the next one, since the lines linear, it'll go in equal steps so couldn't 4000 minutes be $65, since 1000 is$35, 2000 is $45, 3000 could be$55 and 4000, 65? Like I said though, this is a q I'm not too confident with so check to make sure.
This is incorrect. The gradient of the line is delta(y)/delta(x) this is not 2.
The line does however intersect at 25, though:
y-y1 = m(x - x1) is a better method of doing this.
4. (Original post by strangepath)
I am such an idiot, the answer was written right there
dw about it, everyone's done it before
5. (Original post by joostan)
This is incorrect. The gradient of the line is delta(y)/delta(x) this is not 2.
The line does however intersect at 25, though:
y-y1 = m(x - x1) is a better method of doing this.
Sorry I still find the last question really difficult.
6. (Original post by strangepath)
Sorry I still find the last question really difficult.
Which part in particular?
7. (Original post by joostan)
Which part in particular?
the whole question I guess. If you could give formulas or make it into an equation then I might be able to do it.
8. (Original post by strangepath)
the whole question I guess. If you could give formulas or make it into an equation then I might be able to do it.

to find the y-intercept by rearranging into the format y=mx+c
9. I am sorry I just don't get it. I don't know what I should put into the formula. Please help this dumb guy out, I need to due it tomorrow.
10. (Original post by strangepath)
I am sorry I just don't get it. I don't know what I should put into the formula. Please help this dumb guy out, I need to due it tomorrow.
Quoting me makes it easier to spot and don't put yourself down
Now: What is
11. (Original post by joostan)
Quoting me makes it easier to spot and don't put yourself down
Now: What is
is it 45-35?
12. (Original post by strangepath)
I am sorry I just don't get it. I don't know what I should put into the formula. Please help this dumb guy out, I need to due it tomorrow.

Change in y, over change in x with coordinates and
13. (Original post by strangepath)
is it 45-35?
14. (Original post by Robbie242)

Change in y, over change in x with coordinates and
so its m = 45-35/2000-1000
which is m = 0.01?
15. (Original post by strangepath)
so its m = 45-35/2000-1000
which is m = 0.01?
yes though writing it as a fraction is better notation
16. (Original post by strangepath)
so its m = 45-35/2000-1000
which is m = 0.01?
Precisely now proceed by plugging the coordinates and gradient (m) into the straight line equation Remember, you can chose either points, but go with the simpler ones!
17. (Original post by joostan)

to find the y-intercept by rearranging into the format y=mx+c
what is the y and x without the number one attached to it?
18. (Original post by strangepath)
what is the y and x without the number one attached to it?
They are just algebraic constants, so say you have coordinates (2,3) and m=1
19. (Original post by strangepath)
what is the y and x without the number one attached to it?
Pick either point (35,1000) or (45,2000)
These points have both an x-coordinate and a y-coordinate.
So a general point on the line can be said to be the point:
The 1 just makes it a general term.
20. (Original post by Robbie242)
They are just algebraic constants, so say you have coordinates (2,3) and m=1
(Original post by joostan)
Pick either point (35,1000) or (45,2000)
These points have both an x-coordinate and a y-coordinate.
So a general point on the line can be said to be the point:
The 1 just makes it a general term.
so its
y-35 = 0.01(x-1000)
0 = 0.01x -y + 25?

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