anonymous
  • anonymous
Find an exact value. cos 15°
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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katieb
  • katieb
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arindameducationusc
  • arindameducationusc
cos(45-30) using cos(A-B)=cosAcosB+sinAsinB
arindameducationusc
  • arindameducationusc
Got?
anonymous
  • anonymous
cos (45 - 30) = cos45cos30 + sin45sin30 ?

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arindameducationusc
  • arindameducationusc
yes
arindameducationusc
  • arindameducationusc
Can you solve now?
anonymous
  • anonymous
so then would it be cos (45-30) = (radical) 2 / 2 * (radical) 3 / 2 + (radical) 2 / 2 * 1 / 2 ?
anonymous
  • anonymous
would it be \[\sqrt{6} + \sqrt{2} / 4\]
arindameducationusc
  • arindameducationusc
It should be Sqrt[3] - 1/2 Sqrt[2]
arindameducationusc
  • arindameducationusc
1/sqrt(2)*sqrt(3)/2 - 1/sqrt(2)*1/2
arindameducationusc
  • arindameducationusc
=sqrt(3)-1 / 2sqrt(2)
arindameducationusc
  • arindameducationusc
Got it?
anonymous
  • anonymous
thats not one of my answer choices :(
anonymous
  • anonymous
these are my answer choices
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arindameducationusc
  • arindameducationusc
okay let me see....
anonymous
  • anonymous
@lxoser cos(15) To find this value, all you have to do is express 15 as a sum or difference of two known unit circle values. Then, take advantage of the sum/difference identities. cos(a + b) = cos(a)cos(b) - sin(a)sin(b) cos(a - b) = cos(a)cos(b) + sin(a)sin(b) [note: watch how the addition one uses subtraction, and subtraction uses addition] For this case, 15 = 45 - 30. Therefore, cos(15) = cos(45 - 30) And we know what the sine and cosine of 45 degrees and 30 degrees are. Using the cosine difference identity, we get cos(45)cos(30) + sin(45)sin(30) Which we know how to solve. (sqrt(2)/2) (sqrt(3)/2) + (sqrt(2)/2) (1/2) Keep simplifying, [ sqrt(6)/4 ] + [ sqrt(2) / 4 ] [sqrt(6) + sqrt(2)] / 4
anonymous
  • anonymous
its A
anonymous
  • anonymous
so i got it right the first time, thank you so much guys for your time & help! i understand now :-)
anonymous
  • anonymous
i live in florida
anonymous
  • anonymous
is that FLVS?
anonymous
  • anonymous
lol, yes it is
anonymous
  • anonymous
i completely agree!! lol
anonymous
  • anonymous
i like how if you miss one you get an 80 on the homework
anonymous
  • anonymous
yeah i know! like really?
anonymous
  • anonymous
and it brings your grade down like 2-3 points but if you get a 100 it brings it up like .25
anonymous
  • anonymous
lmao omg i feel your pain so much
anonymous
  • anonymous
what math are you in
anonymous
  • anonymous
what math are you in
anonymous
  • anonymous
im in pre-cal honors
anonymous
  • anonymous
if you go to google and type in flvs it got a 2.5 on google but flvs only shows the good ones on the side XD
anonymous
  • anonymous
lol, really?? florida students got it rough lol

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