Question

Find the exact value of the expression without using a calculator.
cos(2tan^-1(12/5))

Thanks

Answer 1

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Answer 2

\[\cos(2\tan^{-1} 12/5)\]

Answer 3

\[Let \tan^-1(12/5)=x\]
cos2x= 2cos^2x-1=2cos^2[tan^-1(12/5)]-1=2(5/13)^2-1=50/169-1=-119/169