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Question
Find the value of cos 2A, A lies in the first quadrant, when tan A `16/63`
Solution
cos 2A = `(1 - tan^2"A")/(1 + tan^2"A")`
= `(1 - (16/63)^2)/(1 + (16/63)^2`
= `((63)^2 - (16)^2)/((63)^2 + (16)^2`
= `((63 + 16) (63 - 16))/(3969 + 256)`
= `(79 xx 47)/4225`
= `3713/4225`
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