Proof of Trig Identity
Date: 7/24/96 at 18:46:58 From: Robert James Spencer Subject: Proof of Trig Identity Dear Dr. Math, I am having trouble proving trig identities. Here is an example: Prove the following is an identity (let t = theta) (sin 2t + sin t)/(cos 2t + cos t + 1) = tan t I tried: (2sin t cos t + sin t)/(2cos^2 t - 1 + cos t + 1) = tan t (2sin t cos t + sin t)/cos t(2cos t + 1)= tan t sin t(2cos t +1)/ cos t(2cos t +1) = tan t *Is this step allowable?* sin t/cos t = tan t tan t = tan t Thanks for your time. Jackie Spencer
Date: 7/25/96 at 6:6:35 From: Doctor Anthony Subject: Re: Proof of Trig Identity Yes, your working is perfectly OK. You can cancel a factor from top and bottom rows as long as it is a factor of the whole top row and whole bottom row. -Doctor Anthony, The Math Forum Check out our web site! http://mathforum.org/dr.math/
Search the Dr. Math Library:
Ask Dr. MathTM
© 1994- The Math Forum at NCTM. All rights reserved.