math
posted by pete .
if sin(theta)=1/4
and pie/2<theta<pie what is the value of cos(theta)

make a rough sketch of a rightangled triangle in the second quadrant with a hypotenuse of 4 and a vertical leg of 1.
(remember sin(angle) = opposite/hypotenuse)
by Pythagoras, the other side must be √15
in the second quadrant the cosine is negative, so
cos(theta) = √15/4
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