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Edutopia
question about the proof of trig addition formulas for cos:
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?
also any sites with a better, easy to understand, definition would be greatly appriciated
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.
but PRQ is only one of the complementary angles, how do i know that it is half of 90?
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...
|dw:1357875756276:dw| Just drawing diagram here
im sorry we got it switched around somewhere its RPQ not PQR
they are proving that RPQ=alpha
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?
OH RPQ is a TRIANGLE! oops
the pi/2 is just radians, i was using degrees. sorry if that is confusing...
no its not i understand radians
aha i see it, thank you very much!
You're welcome! :)