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- anonymous

question about the proof of trig addition formulas for cos:

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- anonymous

question about the proof of trig addition formulas for cos:

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- anonymous

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?

- anonymous

also any sites with a better, easy to understand, definition would be greatly appriciated

- AccessDenied

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.

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- anonymous

but PRQ is only one of the complementary angles, how do i know that it is half of 90?

- AccessDenied

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...

- AccessDenied

|dw:1357875756276:dw|
Just drawing diagram here

- anonymous

im sorry we got it switched around somewhere its RPQ not
PQR

- anonymous

they are proving that RPQ=alpha

- AccessDenied

Since PRQ is a right triangle with right angle PRQ, RPQ and RQP are complementary.

- anonymous

OH RPQ is a TRIANGLE! oops

- AccessDenied

the pi/2 is just radians, i was using degrees. sorry if that is confusing...

- anonymous

no its not i understand radians

- AccessDenied

Ah, okay. :)

- anonymous

aha i see it, thank you very much!

- AccessDenied

You're welcome! :)

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