Question
If cosx/siny = n and cosx/cosy = m, then the value of
cos 2 y is: 1. m 2 /(m 2 + n 2 )2. 1/(m 2 + n 2 )3. n 2 /(m 2 + n 2 )4. 0Solution
Since, cosx = nsiny
(nsiny)/(cosy) = m
ntany = m
tany = m/n
tan 2 y = m 2 /n 2
sec 2 y = 1 + m 2 /n 2 = (m 2 + n 2 )/n 2
cos 2 y = 1/sec 2 y = n 2 /(m 2 + n 2 )
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