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October 23, 2014

October 23, 2014

Posted by **Anonymous** on Tuesday, October 19, 2010 at 11:28pm.

- trig -
**Reiny**, Tuesday, October 19, 2010 at 11:56pmgiven cos x = 4/5

by making a diagram, you should recognize the 3,4,5 right-angles triangle

secondly, the cosine is positive in quadrants I and IV

in I:

sinx = 3/5 , csc x = 5/3

cosx = 4/5 , sec x = 5/4

tanx = 4/3 , cot x = 3/4

you do IV

back to cos(pi over 2-x)=3/5

cos (π/2 - x) = 3/5

(cosπ/2)(cosx) + (sinπ/2)(sinx)= 3/5

sinx = 3/5

(hey, we knew that!)

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