Question
Sun June 26, 2011 By:

answer it

Expert Reply
Sun June 26, 2011
sec ? - tan ? = 4 ------(1)

It is known that sec2?  - tan2?  = 1
So, (sec ? + tan ?) (sec ? - tan ?) = 1
(4) (sec ? + tan ?) = 1
=> (sec ? + tan ?) = 1/4 -----------(2)

Adding (1) + (2), we get,

2sec ? = 4 + (1/4) = 17/4
sec ? =17 / 8
So, cos ? = 8/ 17
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