anonymous
  • anonymous
Prove this identity sin(2A)=2sinAcosA.
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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katieb
  • katieb
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anonymous
  • anonymous
Start by considering 2A as A+A ... does that make you think of any particular theorem?
TuringTest
  • TuringTest
...of course that makes me want to know how to prove the theorem you are thinking of @Tonks
anonymous
  • anonymous
sin(a+a)=sinacosb+cosasinb put the value of a and be here.

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anonymous
  • anonymous
We know that sin(2A) = sin(A + A) sin (A + A) = cosA sinA + cosA sinA = 2 sinA cosA QED
anonymous
  • anonymous
@TuringTest try stacking triangles in the unit circle... or is that for cosine?
TuringTest
  • TuringTest
I know it was some geometric proof like that, I don't remember those darn things...
anonymous
  • anonymous
Is that enough or do you need proof for sin (A + B) = cosA sinB + cosB sinA
anonymous
  • anonymous
http://youtu.be/BlEtOG4NRsg
anonymous
  • anonymous
formula you have given is wrong @micahwood50
TuringTest
  • TuringTest
it's correct
anonymous
  • anonymous
For proof of sin (A + B) = cosA sinB + cosB sinA: http://en.wikipedia.org/wiki/Proofs_of_trigonometric_identities#Sine
anonymous
  • anonymous
http://upload.wikimedia.org/math/3/e/c/3ec0e99aa364deb052280bcd801fcec2.png
TuringTest
  • TuringTest
yep, that's the one...
anonymous
  • anonymous
@muhammad9t5 It's the same. Your point is?
TuringTest
  • TuringTest
perhaps you are neglecting the fact that multiplication is commutative muhammad?
anonymous
  • anonymous
|dw:1350147756505:dw|
anonymous
  • anonymous
ok i got it!! he has just rearranged the places of cos and sin.
TuringTest
  • TuringTest
in English that's called the commutative property of addition.
anonymous
  • anonymous
yup.
anonymous
  • anonymous
Yeah, sorry about that, though. It's easier for me to remember this formula this way.
anonymous
  • anonymous
@micahwood50 can this destroy the problem of sin(45-30) solve with your formula.
anonymous
  • anonymous
cos45*sin30-cos45sin30
anonymous
  • anonymous
Well, with minus, it's different story.
anonymous
  • anonymous
ok do sin(45+30)=cos45sin30+cos30sin45
anonymous
  • anonymous
Yeah, I got it. Thanks, though.
anonymous
  • anonymous
bro never mind if i disturb you! Accept just like the game of trig!
anonymous
  • anonymous
@muhammad9t5 I know the formulas, you don't have to correct me. Thanks, though.

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