Jul20 comment Deriving the sum-to-product identities Thank you for your answer! Jul20 accepted Deriving the sum-to-product identities Jul20 comment Deriving the sum-to-product identities Thank you, that was a very concise and clear explanation Jul20 comment Deriving the sum-to-product identities @heropup, thanks, i see what you mean now.. Jul20 comment Deriving the sum-to-product identities @AndréNicolas, Why is it that I need to use different letters? Jul20 asked Deriving the sum-to-product identities Jul20 comment Soviet Russian Mathematical Books Just to add to this, a publisher going by the name of MIR seems to have been a big player in publishing texts by prominent Soviet mathematicians, however it is very difficult to get hold of those books today, some of them can be found on the site mirtitles.org Jul14 revised A few questions regarding the cosine difference identity added 65 characters in body Jul14 accepted Applying the cosine even identity to the cosine difference identity Jul14 comment Applying the cosine even identity to the cosine difference identity Just what I was looking for! Jul14 comment Applying the cosine even identity to the cosine difference identity Yes you're right! Thanks! Jul14 asked Applying the cosine even identity to the cosine difference identity Jul14 revised A few questions regarding the cosine difference identity added 141 characters in body Jul14 revised A few questions regarding the cosine difference identity added 141 characters in body Jul14 comment A few questions regarding the cosine difference identity I manipulated the equation I get that, however what I square rooted the R.H.S of the equality: $$2 - 2\cos (\alpha - \beta )$$; there hasnt been much manipulation done to this (apart from using the pythagorean identity to simplify some trig expressions), would that give me the length of the two chords? Jul14 awarded Popular Question Jul13 comment A few questions regarding the cosine difference identity I dont understand how it's possible to have a negative cosine value in the first quadrant? Could you explain a little more on this please. Jul13 asked A few questions regarding the cosine difference identity Jul13 comment How can I understand and prove the “sum and difference formulas” in trigonometry? (cos(a ± b) = …, etc.)? Thank you, this looks like a neat application Jul13 comment How can I understand and prove the “sum and difference formulas” in trigonometry? (cos(a ± b) = …, etc.)? with program did you draw this diagram?