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Edutopia

  • 2 years ago

question about the proof of trig addition formulas for cos:

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  1. Edutopia
    • 2 years ago
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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?

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

  3. AccessDenied
    • 2 years ago
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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.

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

  5. AccessDenied
    • 2 years ago
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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...

  6. AccessDenied
    • 2 years ago
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    |dw:1357875756276:dw| Just drawing diagram here

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

  8. Edutopia
    • 2 years ago
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    they are proving that RPQ=alpha

  9. AccessDenied
    • 2 years ago
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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?

  10. Edutopia
    • 2 years ago
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    OH RPQ is a TRIANGLE! oops

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

  12. Edutopia
    • 2 years ago
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    no its not i understand radians

  13. AccessDenied
    • 2 years ago
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    Ah, okay. :)

  14. Edutopia
    • 2 years ago
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    aha i see it, thank you very much!

  15. AccessDenied
    • 2 years ago
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    You're welcome! :)

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