Question

Algebraically find the value of: 10 cot⁡(cot^(-1)⁡3+cot^(-1)⁡7+cot^(-1)⁡13+cot^(-1)⁡21 )

Answer 1

Take a look here:

http://www.maths.surrey.ac.uk/hosted-sites/R.Knott/Fibonacci/fibpi.html

and scroll down to Sec. 6.2

Answer 2

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