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Edutopia

question about the proof of trig addition formulas for cos:

  • one year ago
  • one year ago

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  1. Edutopia
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    sorry about the scrolling: http://en.wikipedia.org/wiki/Proofs_of_trigonometric_identities on the part with the diagram for trig addition formulas, where does "RPQ = (PI/2) - RPQ" come from?

    • one year ago
  2. Edutopia
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    also any sites with a better, easy to understand, definition would be greatly appriciated

    • one year ago
  3. AccessDenied
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    RPQ = pi/2 - RQP pi/2 radians is 90 degrees. RPQ = 90 degrees - RQP which we can see because that triangle is a right triangle, so the other two angles have to be complementary to add up to 180 degrees interior.

    • one year ago
  4. Edutopia
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    but PRQ is only one of the complementary angles, how do i know that it is half of 90?

    • one year ago
  5. AccessDenied
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    I believe PRQ is meant to be a right angle, 90 degrees or pi/2 radians, although it doesn't appear to be indicated as such...

    • one year ago
  6. AccessDenied
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    |dw:1357875756276:dw| Just drawing diagram here

    • one year ago
  7. Edutopia
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    im sorry we got it switched around somewhere its RPQ not PQR

    • one year ago
  8. Edutopia
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    they are proving that RPQ=alpha

    • one year ago
  9. AccessDenied
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    Since PRQ is a right triangle with right angle PRQ, RPQ and RQP are complementary. <RPQ + <RQP + <PRQ = 180 <RPQ + <RQP + 90 = 180 <RPQ + <RQP = 90 <RPQ = 90 - <RQP Would that make sense?

    • one year ago
  10. Edutopia
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    OH RPQ is a TRIANGLE! oops

    • one year ago
  11. AccessDenied
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    the pi/2 is just radians, i was using degrees. sorry if that is confusing...

    • one year ago
  12. Edutopia
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    no its not i understand radians

    • one year ago
  13. AccessDenied
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    Ah, okay. :)

    • one year ago
  14. Edutopia
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    aha i see it, thank you very much!

    • one year ago
  15. AccessDenied
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    You're welcome! :)

    • one year ago
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