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need help w/proof cos(ab)= (cosA*cosB)+(sinA*sinB)Posted by Jon_ P on February 27, 19100 at 23:53:14: Can someone help me prove this identity? I have some trig. teaching software but all it says is that the distance formula, for the chord that seperates the angles can be used to prove it. It's important because it form the basis for many other identities use in integration techniques. Such as the double angle and product identities. Thank a bunch folks. Post a Followup
