I love maths - arctan(1/3)+arctan(1/2)=arctan1...As the total angle made by green and blue angle is nothing but an angle created by diagonal of a square (which is π/4). | Facebook
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trigonometry - What is the value of $\arctan(1/2)+\arctan(1/5)+\arctan(1/8)$? - Mathematics Stack Exchange
The construction of arctan(1/2)/π
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How to show that arctan 1/3+arctan 1/5=arctan 4/7 - Quora
Esercizio svolto: Studio di una funzione arcotangente | matematica & oltre
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How to show that arctan 1/3+arctan 1/5=arctan 4/7 - Quora
L'arcotangente spiegato in modo semplice - Andrea Minini