Prove that cos^-1(1/5)+cos^-1(5/7)+cos^-1(19/35) = Pie without the use of a calculator? How would I do this?

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- May 3rd 2009, 04:04 PMzweevuProving Trig Identities.
Prove that cos^-1(1/5)+cos^-1(5/7)+cos^-1(19/35) = Pie without the use of a calculator? How would I do this?

- May 3rd 2009, 08:57 PMmr fantastic