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# how do i find the exact value of cos x when 8cos x cosec^2 x = 3 watch

1. how do i find the exact value of cos x when 8cos x cosec^2 x = 3
i know that its 1/3 but not sure in teh slightest on how to get there. this was in the last C3 paper i did
2. from what i remember( wierd enough) cosec^2x = 1-sec^2x or something similar there is a formula... and the sec^2x has a formula probaly which you change to cosx then you bring the 3 on to the left and factorise...
how do i find the exact value of cos x when 8cos x cosec^2 x = 3
i know that its 1/3 but not sure in teh slightest on how to get there. this was in the last C3 paper i did
from what i remember( wierd enough) cosec^2x = 1-sec^2x or something similar there is a formula... and the sec^2x has a formula probaly which you change to cosx then you bring the 3 on to the left and factorise...
4. this was the ocr exam question today wasnt it
i got stuck on it for aaaages but i think (hope it worked out ok)

cosec^2 = 1+ cot^2
sub that in
8cosx X 8(cos^2/sin^2)=3
8cosx X 8(cos^2/1-cos^2)=3

8cosx-8cos^3 + 8cos^3 = 3 - 3cos^2

3cos^2+8cos-3=0
(3cos-1)(cos+3)=0
cos = 1/3 as cos =-3 is undefined

hhope this is right and it helps (obviously cant do much about it now good luck)
5. I got this right as well hehe, this paper is well hard I [rainbow]******[/rainbow] up so many questions
6. thanks alot, but between these 2 steps im a bit confused, can you break it down a bit more? (sorry im a bit slow :P)

8cosx X 8(cos^2/1-cos^2)=3

8cosx-8cos^3 + 8cos^3
7. ah this is a clever question;

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