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

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# 2001 - Paper 1 - Q11(C)

Started by Max018, May 16 2004 09:20 AM

7 replies to this topic

### #1

Posted 16 May 2004 - 09:20 AM

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

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.

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

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

Posted 18 May 2004 - 09:39 AM

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

### #5

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!

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### #6

Posted 18 May 2004 - 02:59 PM

ach theres always other ways round it

### #7

Posted 18 May 2004 - 04:21 PM

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

### #8

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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