Posted by shandra on Monday, January 2, 2012 at 10:04pm.
Given tan theta=8/5 and sin theta < 0, find cos theta.

Mathprecalculus  Reiny, Monday, January 2, 2012 at 10:40pm
if tanØ < 0 and sinØ < 0 , then Ø must be in quad IV
from tanØ = 8/5 in IV, we have x = 5, y = 8
r^2 = 25+64 = 89
r = √89
then cosØ = 5/√89
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