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Mathematics 15 Online
OpenStudy (anonymous):

Determine the exact value of cos18 (degrees). Hint:sin2x= cos3x where x=18 degrees.

OpenStudy (mathsolver):

cos(18)=0.951056516 If thats what you wanted

OpenStudy (anonymous):

No, I am looking for the exact value.

OpenStudy (dumbcow):

using your hint you could also say sin(4x) = cos(x) if x=18

OpenStudy (anonymous):

using your identity sin30 = cos3(18) sin 30 = 0.5

OpenStudy (anonymous):

cos3(18) = 0.5

OpenStudy (dumbcow):

no...cos(54) = .5877

OpenStudy (anonymous):

yea - my mistake

OpenStudy (anonymous):

Thanks, but I still don't know how to come up with the answer...

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