anonymous
  • anonymous
Find an exact value: cos(pi/12)
Trigonometry
  • Stacey Warren - Expert brainly.com
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SOLVED
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chestercat
  • chestercat
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mathmate
  • mathmate
let y=cos(pi/12), then apply the double angle formula: cos^2(x)-sin^2(x)=cos(2x) or, substituting sin^2(x)+cos^2(x)=1, 2cos^2(x)-1=cos(2x) cos^2(x)=(1+cos(2x))/2 let x=pi/12 then cos^2(pi/12)=(1+cos(pi/6))/2 Since cos(pi/6) is known to be sqrt(3)/2, cos(pi/12)=sqrt((1+sqrt(3)/2)/2)
anonymous
  • anonymous
im sorry but thats not one of my options
anonymous
  • anonymous
i somehow have to use the sum and difference formulas

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mathmate
  • mathmate
Are they in numerical values?
anonymous
  • anonymous
yes they all have sqrt6 and sqrt2 over 4 but with different signs +/-
mathmate
  • mathmate
cos^2(x)-sin^2(x)=cos(2x) is from the double angle formula.
anonymous
  • anonymous
how would you split pi/12? i think thats what i need to do?
mathmate
  • mathmate
You will need to evaluate each option to see if it evaluates to: sqrt((1+sqrt(3)/2)/2) which can be written as sqrt((2+sqrt(3)/4) or sqrt(2+sqrt(3))/2 Why don't you post the options if you're not sure?
anonymous
  • anonymous
ok i think i got it thanks!!
mathmate
  • mathmate
yw! :)

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