circle geometry question help

Original post by madfish

Hey guys a little help with this circle geometry question would be appreciated:

Didn't I list the approach for this one yesterday?

Reply 3

OP

Original post by TenOfThem

Didn't I list the approach for this one yesterday?

Yea you did but I couldn't find it as my ISP would not load my "watched threads" page for some obscure reason. Sorry about that :colondollar:

Reply 4

BabyMaths

Original post by madfish

Yea you did but I couldn't find it as my ISP would not load my "watched threads" page for some obscure reason. Sorry about that :colondollar:

http://www.thestudentroom.co.uk/showthread.php?p=41445938&highlight=

I just looked at a few of TenOfThem's posts. Wasn't hard to find.

Reply 5

Original post by madfish

Yea you did but I couldn't find it as my ISP would not load my "watched threads" page for some obscure reason. Sorry about that :colondollar:

ok

Thought that it was familiar

Reply 6

Original post by BabyMaths

I just looked at a few of TenOfThem's posts. Wasn't hard to find.

Stalker

Reply 7

So now you have the co ordinates (well should have).

Complete the squares to find the centre of the circle. Then use that to find the centre.

Then calculate the gradients of each radius connecting to the points.

The tangents will be perpendicular to those.

Reply 8

BabyMaths

Original post by TenOfThem

Stalker

I stalk all the best people. :tongue:

Reply 9

OP

Original post by BabyMaths

http://www.thestudentroom.co.uk/showthread.php?p=41445938&highlight=

I just looked at a few of TenOfThem's posts. Wasn't hard to find.

Yea I know, but my computer pooped itself last night and would not load up certain pages so it was a lot more convenient at the time to create a new thread :redface:

By the way, Thank you for helping me in all my maths threads. I am self teaching and your input helps me so much! I can't stress enough how grateful I am! :smile:

Thank you

Reply 10

Original post by madfish

Yea I know, but my computer pooped itself last night and would not load up certain pages so it was a lot more convenient at the time to create a new thread :redface:

By the way, Thank you for helping me in all my maths threads. I am self teaching and your input helps me so much! I can't stress enough how grateful I am! :smile:

Thank you

Me too!

Although I think that's stupid. How on earth can a college be allowed to require additional maths?!

I didn't even get to do that...

Reply 11

OP

Original post by L'Evil Fish

So now you have the co ordinates (well should have).

Complete the squares to find the centre of the circle. Then use that to find the centre.

Then calculate the gradients of each radius connecting to the points.

The tangents will be perpendicular to those.

Thank you, brother. haha. I got (1,-4) and (5, -4) for the two points and (3,-2) for the centre of the circle.

I keep get a gradient of 1 and -1, giving me -1 and 1 gradients for the tangents. But when I solve I do not get the answer in my textbook.. Are these the correct coordinates I have found? :colondollar:

Reply 12

OP

Original post by L'Evil Fish

Me too!

Although I think that's stupid. How on earth can a college be allowed to require additional maths?!

I didn't even get to do that...

And you too! I really do appreciate it soo much! Very kind of you all :smile:

I know

I am so worried that I won't get it all done in time.. the only thing that gives me hope is the fact I have 2 weeks to revise C2 after all my other exams are finished :cool:

Reply 13

Original post by madfish

Thank you, brother. haha. I got (1,-4) and (5, -4) for the two points

Since we want points on the x-axis

And we set y=0

Why would y suddenly be -4

Reply 14

Original post by madfish

Thank you, brother. haha. I got (1,-4) and (5, -4) for the two points and (3,-2) for the centre of the circle.

I keep get a gradient of 1 and -1, giving me -1 and 1 gradients for the tangents. But when I solve I do not get the answer in my textbook.. Are these the correct coordinates I have found? :colondollar:

where did the -4 come from?

Original post by madfish

And you too! I really do appreciate it soo much! Very kind of you all :smile:

I know

I am so worried that I won't get it all done in time.. the only thing that gives me hope is the fact I have 2 weeks to revise C2 after all my other exams are finished :cool:

Hopefully it'll be okay.

Reply 15

OP

Original post by TenOfThem

Since we want points on the x-axis

And we set y=0

Why would y suddenly be -4

How do find the gradients so I can use the equation y-y1=m(x-x1)? That's what I am struggling to figure out :s-smilie:

Reply 16

OP

Original post by L'Evil Fish

where did the -4 come from?

Hopefully it'll be okay.

I am not too sure.. I know the x coordinates are 1 and 5 but I am not sure what to do next.. I presume you need to find a gradient of some sort?

And thank you :smile:

Reply 17

x^2-6x+5=0
(x-5)(x-1) = 0
x = 5 or 1

So: (1,0) or (5,0)

x^2 + y^2 -6x + 4y + 5 = 0
(x-3)^2 + (y+2)^2 = 8

Centre: (3,-2)

y - y_1 = m(x-x_1)
(0+2)/(5-3) = m
m = 1

So gradient is 1 for that radius.

y - y_1 = m(x-x_1)
(-2-0)/(3-1) = m
m = -1

So your answers are right there

Now to find equation of tangents:

The gradients have a product of -1.

(5,0) gradient of radius was 1. So tangent will be -1.

y = -1(x-5) can you do the.other?

(edited 11 years ago)

Reply 18