How do you evaluate $cos ((7 pi)/3 + (15 pi)/4)$ ?

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Answer 1 · 2016-06-04T16:57:04

$=(sqrt 3+1)/(2 sqrt 2)$

$cos ((7pi)/3+(15pi)/4)$

$=cos (2pi+pi/3 + 4pi-pi/4)$

$=cos(6pi+(pi/3--pi/4))$

$=cos (pi/3-pi/4)$

$=cos(pi/3)cos(pi/4)+sin(pi/3)sin(pi/4)$

$=(1/2)(1/sqrt 2)+(sqrt 3/2)(1/sqrt 2)$

$=(sqrt 3+1)/(2 sqrt 2)$

How do you evaluate cos ((7 pi)/3 + (15 pi)/4)cos ((7 pi)/3 + (15 pi)/4)?