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# P3/C4 question watch

1. hi,
can anyone do part iii) of the attached question? thanks
part i) is (x-8)² + (y-1)² = 16
ive done part 2: (-5/12) < m < (3/4)
im stuck on part 3.
thanks
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2. (Original post by Undry1)
hi,
can anyone do part iii) of the attached question? thanks
part i) is (x-8)² + (y-1)² = 16
ive done part 2: (-5/12) < m < (3/4)
im stuck on part 3.
thanks
Let c be circle centre.

CA=4
CO = √65

So AO = 7 (Pythag)

tan AOC = 4/7

AOB = 2AOC

Double Angle tan formula

Tan 2t = 2tant/(1-tan²t)

Tan 2t = (8/7)/(33/49)
= 56/33

Aitch
3. Here's another method.

=> tan(AOx) = 3/4
=> tan(BOx) = 5/12

So:
tan(AOB) = tan(AOx+BOx)
= [tan(AOx) + tan(BOx)]/[1 - tan(AOx)tan(BOx)]
= (3/4 + 5/12)/(1 - 15/48)
= 56/33
4. ah of course..
i got to the tan theta = 4/7 part
got confused after that
thanks

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