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2001 - Paper 1 - Q11(C) - HSN forum

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2001 - Paper 1 - Q11(C)


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#1 Max018

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Posted 16 May 2004 - 09:20 AM

Hi all,

Great work on the solution, I'm down to 2(x² - 4x - 8) = 0 but I have never seen the equation -b±√b² - 4ac/2a in my puff I believe, and if I have its been a looonng while since I've used it. Any other way (using more farmiliar higher notes?) that this can be finished off?

Thanks,
Paolo

QUOTE
Points of intersection means you can subsitute the y = x + 5 equation into the circle equation:

x² + (x + 5)² - 8x - 10(x + 5) + 9 = 0
x² + (x + 5)(x + 5) - 8x - 10x - 50 + 9 = 0
x² + x² + 10x + 25 - 8x - 10x - 41 = 0
2x² - 8x - 16 = 0
2(x² - 4x - 8) = 0

Then using the quadratic formula you can solve for x:

-b±√b² - 4ac/2a

a = 1
b = -4
c = -8

Substituting these values in should give:

4±√48/2

2 ±(√48/2)
2±(√4√3/2)
2±√2√3



#2 AndyW

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Posted 16 May 2004 - 10:11 PM

You can use the technique of Completing the Square.

2(x² - 4x - 8) = 0
x² - 4x - 8 = 0

x² - 4x = 8
(x-2)² = 8 + 4
x-2 = +/- root12
x = 2 +/- root4*root3
x = 2 +/- 2root3

The final part of what you've quoted above has some errors.

#3 Dave

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Posted 17 May 2004 - 06:49 PM

are you entirely sure you have never seen it before because its SG as far as i know and i think i used it in the exam last year but not entirely sure

If i am not here i am somewhere else



#4 George

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Posted 18 May 2004 - 09:39 AM

Yes, the quadratic formula is used in Standard Grade - the equation is given in the exam.

#5 Ally

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Posted 18 May 2004 - 12:03 PM

QUOTE (George @ May 18 2004, 09:39 AM)
Yes, the quadratic formula is used in Standard Grade - the equation is given in the exam.

Are you referring to the Standard Grade exam, as it's not given in the Higher exam.

So Max you would probably need to learn it before Friday!

#6 Max018

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Posted 18 May 2004 - 02:59 PM

ach theres always other ways round it smile.gif

#7 james1

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Posted 18 May 2004 - 04:21 PM

You use quadratic formula for so many things in AH Maths.

#8 George

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Posted 18 May 2004 - 10:00 PM

I think it's assumed at Higher and AH that you know the quadratic formula. It's not too hard to learn, given that most of it is the discriminant.





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