Question #18095

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Answer 1 · 2018-01-21T22:14:29

#cos(2y) = 7/25#

Given: #sec(y) = 5/4#

Then #cos(y) = 4/5#

Using the identity #cos(2y) = 2cos^2(y)-1#:

#cos(2y) = 2(4/5)^2-1#

#cos(2y) = 2(16/25)-1#

#cos(2y) = 32/25-1#

#cos(2y) = 7/25#