Verifying Trigonometric Identities Involving Sum & Difference

I work through some examples of verifying trig identities that require the use of sum & difference identities of Sine, Cosine, and Tangent I was corrected that what I am trying to prove should not be within the body of the proof. This implies it has already been assumed to be true. So proofs should be shown like this example: cos^2(x)(tan^2(x)+1)=1 Proof: cos^2(x)(tan^2(x)+1)=cos^2(x)*sec^2(x) =cos^2(x)(1/cos^2(x)) =1 Check out http://www.ProfRobBob.com/, there you will find my lessons organized by class/subject and then by topics within each class. Find free review test, useful notes and more at http://www.mathplane.com/ If you'd like to make a donation to support my efforts look for the "Tip the Teacher" button on my channel's homepage    / profrobbob