Chittesh14
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Hello, can someone please help me out here...

How do you work out the equation of a curve using its points of intersection
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Kevin De Bruyne
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(Original post by Chittesh14)
Hello, can someone please help me out here...

How do you work out the equation of a curve using its points of intersection
Intersection with what?

Please post a question that you're stuck with.
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Chittesh14
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(Original post by SeanFM)
Intersection with what?

Please post a question that you're stuck with.
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Part c

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Kevin De Bruyne
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(Original post by Chittesh14)
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Part c

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Think about the information that you've been given in the question and then what you've found in part b.
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ubisoft
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(x-A)(x-B)=0
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Chittesh14
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(Original post by ubisoft)
(x-A)(x-B)=0
I kind of understand that a bit.
What would A and B be in that equation. They both have two coordinates, x and y coordinates. What is A in the bracket and what is B in the other bracket?


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ubisoft
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(Original post by Chittesh14)
I kind of understand that a bit.
What would A and B be in that equation. They both have two coordinates, x and y coordinates. What is A in the bracket and what is B in the other bracket?


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The x coordinate of the intercept. The y intercept is 0 for both as it's the x intercept.
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Chittesh14
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(Original post by ubisoft)
(x-A)(x-B)=0
If you are trying to say (x+3)(x-2)=0,

I understand that, but when I expand it, I get a different answer to the actual answer.


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Chittesh14
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(Original post by ubisoft)
The x coordinate of the intercept. The y intercept is 0 for both as it's the x intercept.
Sorry, I think I understood the part above, just it didn't give me the answer?


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Chittesh14
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(Original post by ubisoft)
The x coordinate of the intercept. The y intercept is 0 for both as it's the x intercept.
Maybe, the answer in the book is incorrect.
The answer in the book is x^2 + 2x - 5


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TeeEm
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(Original post by Chittesh14)
Maybe, the answer in the book is incorrect.
The answer in the book is x^2 + 2x + 5


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which part?
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Chittesh14
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(Original post by TeeEm)
which part?
C


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Plücker
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(Original post by Chittesh14)
Maybe, the answer in the book is incorrect.
The answer in the book is x^2 + 2x + 5


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The correct answer for part c is y=x^2+2x-5. The book has the wrong answer.
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TeeEm
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if you have the coordinates of A and B

use A first
substitute the x and the y coordinate of A into the quadratic and you will get a linear equation in p and q.

then you substitute the x and the y coordinate of B into the quadratic and you will get a second linear equation in p and q.

you solve simultaneously to get p and q
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Chittesh14
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(Original post by TeeEm)
if you have the coordinates of A and B

use A first
substitute the x and the y coordinate of A into the quadratic and you will get a linear equation in p and q.

then you substitute the x and the y coordinate of B into the quadratic and you will get a second linear equation in p and q.

you solve simultaneously to get p and q
I was actually planning to do that, but I thought it'll be incorrect lol.


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Chittesh14
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(Original post by BuryMathsTutor)
The correct answer for part c is y=x^2+2x-5. The book has the wrong answer.
Sorry, I thought I edited the typo. The book answer was x^2 + 2x - 5.


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Chittesh14
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(Original post by TeeEm)
if you have the coordinates of A and B

use A first
substitute the x and the y coordinate of A into the quadratic and you will get a linear equation in p and q.

then you substitute the x and the y coordinate of B into the quadratic and you will get a second linear equation in p and q.

you solve simultaneously to get p and q

I'm kind of confused here.

I've got two equations when I substituted the values from the A and the B coordinates.

A: -11 = px + q
B: -1 = px + q


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TeeEm
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(Original post by Chittesh14)
I'm kind of confused here.

I've got two equations when I substituted the values from the A and the B coordinates.

A: -11 = px + q
B: -1 = px + q


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there should be no x, x was substituted with the x from each of the 2 coordinates from A and B
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Chittesh14
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(Original post by TeeEm)
there should be no x, x was substituted with the x from each of the 2 coordinates from A and B
Oops, I've done it now.
Q = -5 and p = 2

X^2 + 2x - 5

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Chittesh14
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Thanks everyone


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