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
L'arcotangente spiegato in modo semplice - Andrea Minini
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Funzione ArcoTangente | iMathematica
Dave Richeson on X: "Euler proved that π/4=arctan(1/2)+arctan(1/3), which can be used for computing digits of π (using the arctangent series). I wondered if I could prove it without using a trig