anonymous
  • anonymous
Find the exact value by using a half-angle identity. cos(5π/12) I know someone knows how to do this! if you could explain too, that'd be great!
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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katieb
  • katieb
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anonymous
  • anonymous
os 5π/12 cos ((5 pi/6)/2) = +/- sqrt( (1+cos (5 pi/6))/2 ) cos(5 pi/6) = -sqrt(3)/2 cos (5 pi/12) = +/- sqrt( (2/2-sqrt(3)/2)/2 ) cos (5 pi/12) = +/- sqrt( ((2-sqrt(3))/2)/2 ) cos (5 pi/12) = sqrt( ( (2-sqrt(3))/4 ) ) 5 pi/12 is in quadrant 1 so we choose the + sign because cos is positive there
anonymous
  • anonymous
thank you!!
anonymous
  • anonymous
your welcome

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anonymous
  • anonymous
wait did you like re-expand the problem after cos(5 pi/6) = -sqrt(3)/2
anonymous
  • anonymous
most of these problems are some identities written on the unit circle.
anonymous
  • anonymous
okay.. well can you please explain each of the steps this person just gave me? i would reaaaalllyyyy appreciate it
anonymous
  • anonymous
ok so 5pi/12 is 75 degrees rite
anonymous
  • anonymous
i guess.. lol is it?
anonymous
  • anonymous
pi is 180 degrees.lol you know that rite and u muliply tht by 5 and get 900 and divide 12 and you get 75 degrees
anonymous
  • anonymous
okay but what does the 75 degrees have to do with the formula?
anonymous
  • anonymous
just to make ur question simpler... for example lets say it asked u for the cos of pi/6 which is 30 degrees.
anonymous
  • anonymous
there is some thing called the unit circle and it has this angles from 30,45,60,90 upto 360.. and since we have cos of Pi/6 which is 30 degrees. we can look at the unit circle for the cosine of 30 degrees and find it
anonymous
  • anonymous
@Dwade03 WHATS THE ANSWER?! D:
anonymous
  • anonymous
how is it done using half angle identity formula?!
anonymous
  • anonymous
ok so since they asked for cos(75) we can use the formula of using two angles to create that angle of 75. in this case we can use cos(45+35). u get tht?
Lukecrayonz
  • Lukecrayonz
@ganeshie8
anonymous
  • anonymous
so what in the world is the final answer? Is it cos(75)?

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