How do you evaluate the expression $cos (7/4 pi)$ ?

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Answer 1 · 2016-05-22T22:13:34

$sqrt2/2$

Trig table and unit circle -->
$cos ((7pi/4) = cos (-pi/4 + (8pi)/4) = cos (-pi/4 + 2pi) = cos (-pi/4) = cos (pi/4) = sqrt2/2$

How do you evaluate the expression cos (7/4 pi)cos (7/4 pi)?