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How do you evaluate $cos [5(pi)/4]$ ?

1 Answer

$phi$

Jan 27, 2016

$cos[5(pi/4)]=-sqrt2/2$

Explanation:

$pi$ $radians=180^circ$

$rarrcos[5(pi/4)]$

$rarrcos[5(180^circ/4)]$

$rarrcos[5(45^circ)]$

$rarrcos(225^circ)=-sqrt2/2$ Use the unit circle

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