Question #f9549

1 Answer
Daniel L.
Sep 3, 2015

If #sin theta=2/3# then #cos theta=sqrt(5)/3# or #cos theta=-sqrt(5)/3#

Explanation:

For every nagle #theta# following equality is true:

#sin^2theta+cos^2theta=1#

If we substitute #sin theta=2/3# we get:

#(2/3)^2+cos^2theta=1#

#4/9+cos^2theta=1#

#cos^2theta=1-4/9#

#cos^2theta=5/9#

#costheta=+-sqrt(5)/3#

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