Dont understand last bit of this circles question

Q8 part b ii in this PDF: http://www.madasmaths.com/archive/iygb_practice_papers/c2_practice_papers/c2_t.pdf

Solution to the question is here: http://www.madasmaths.com/archive/iygb_practice_papers/c2_practice_papers/c2_t_solutions.pdf

Reply 1

LelouchViRuge

7

Original post by TSRforum

Q8 part b ii in this PDF: http://www.madasmaths.com/archive/iygb_practice_papers/c2_practice_papers/c2_t.pdf

Solution to the question is here: http://www.madasmaths.com/archive/iygb_practice_papers/c2_practice_papers/c2_t_solutions.pdf

Do you not understand what he has done?

(edited 7 years ago)

Reply 2

Gregorius

14

Original post by TSRforum

Q8 part b ii in this PDF: http://www.madasmaths.com/archive/iygb_practice_papers/c2_practice_papers/c2_t.pdf

Solution to the question is here: http://www.madasmaths.com/archive/iygb_practice_papers/c2_practice_papers/c2_t_solutions.pdf

Where in particular do you get stuck?

You have worked out in the first part that the centre of C1 is at (9, -k/2) and it has radius

\sqrt{k^2/4 - 9}

. You then work out that C2 has centre at (1,1) with radius 6. You can therefore work out the length of the line joining the centres, and from thence work out what value of k is consistent with the circles just touching as shown.

Dont understand last bit of this circles question

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