anonymous
  • anonymous
what is the exact value of cos 15
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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katieb
  • katieb
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kymber
  • kymber
You have to use your calculator, type cos(15)
Shayaan_Mustafa
  • Shayaan_Mustafa
it can be find out by calculation by using of derivative.
anonymous
  • anonymous
what is the exact value of cos 15

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kymber
  • kymber
You may have a scientific calculator at home, or here's a nice online one: http://www.ecalc.com/ type cos(15) into the calculator to get the exact value of cos15.
anonymous
  • anonymous
i have to break it down
anonymous
  • anonymous
in steps
kymber
  • kymber
Oh. Well I thought you always had to use a calculator. Sorry! Maybe there's a figure to go along with it?
anonymous
  • anonymous
maybe its ok thank you
anonymous
  • anonymous
we need the exact value, we can use the identity: \[\cos(A-B) = \cos(A)\cos(B) + \sin(A)\sin(B)\] let A= 45 and B= 30 from an equilateral triangle we can see \[\cos(30) = \sin(60) = \frac{\sqrt{3}}{2}\]and\[\sin(30)=\cos(60) = \frac{1}{2}\] |dw:1333480959140:dw|and from this right angled triangle we can see that \[\cos(45) = \sin(45)=\frac{1}{\sqrt{2}}\]|dw:1333481210156:dw| put these in the first formula and you can get the exact value

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