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Core Mathematics 3; Trigonometry; Exercise 6C; Q8

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1. In the diagram AB = 6 cm is the diameter of the circle and BT is the tangent to the circle at B. The chord AC is extended to meet this tangent at D and angle DAB = theta
a) Show that CD = 6 (sec[theta]-cost[theta]

So i have seen the answer and how to get to it. I understand that

what i can't understand is why

cos theta = AC/6.

Thanks a detailed work through and explanation would be appreciated.
2. Never mind. Found the right angle triangle ABC. whoops
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3. Wait, are you seriously doing A Level Math at 3am in the morning?
4. (Original post by postexamtalk)
Wait, are you seriously doing A Level Math at 3am in the morning?
5. (Original post by postexamtalk)
Wait, are you seriously doing A Level Math at 3am in the morning?
Haha, where i am it was 5:00am.
6. (Original post by Paranoid_Glitch)
Haha, where i am it was 5:00am.
Ohhh 5am, that totally makes it normal
7. You did it wrong. The answer was 4.72.
8. (Original post by MersennePrime)
You did it wrong. The answer was 4.72.
Sorry which part?
9. (Original post by postexamtalk)
Ohhh 5am, that totally makes it normal
Have to get that A* though.
10. (Original post by Paranoid_Glitch)
Sorry which part?
The part before you divide the equation by 3.

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