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What is the exact value of cos 5pi/4 radians?

User Dennism
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1 Answer

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-Radical two (square root of two)/2
Because:
5pi/4 = 225 the reference angle for that is 45 degrees, cos 45 = Radical two (square root of two)/2 and because 225 is in quadrant three and only tangent is positive in quadrant 3, the cos is negative
User BiTOk
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