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Question
if `cos theta = 5/13` where `theta` is an acute angle. Find the value of `sin theta`
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Solution
`cos theta = 5/13`
`sin^2 theta = 1 - cos^2 theta = 1 - 25/169 = 144/169`
`sin theta = +- 12/13` as `theta` is acute, therefore `sintheta` must be positive
`:. sin theta = 12/13`
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