# The Basel Problem

This identity is usually proved by induction, here is the real ‘frontal attack’ from Euler who gave the first convergent sum of (pi^2/6) for Zeta (2).

The Basel Problem is:
\$latex displaystyle sum_{k=1}^{infty} frac {1}{k^2} = frac {{pi}^2}{6}\$

Euler was 28 years old when he proved that it converged.

The Basel Problem is also called the Riemann Zeta function: ζ(2).

He studied the function sin x which has zeroes,
i.e. sin x= 0 for
\$latex x=npi, n = 0,pm1,pm 2, pm 3…\$

In other words, we can factor sin x this way:
\$latex sin x = x.(1+frac {x}{pi}) .(1-frac {x}{pi}).(1+frac {x}{2pi}). (1-frac {x}{2pi}).(1+frac {x}{3pi}). (1-frac {x}{3pi})…
&s=3\$

Note: the right side any factor = 0 when
\$latex x=npi, n = 0,pm1,pm 2, pm 3…\$

\$latex frac {sin x}{x}
= (1-frac {x^2}{1^{2}{{pi}^2}}).
(1-frac {x^2}{2^{2}{{pi}^2}}).
(1-frac {x^2}{3^{2}{{pi}^2}})…
&s=3
\$

Note: \$latex (1+a).(1-a)= 1 – a^{2}\$

From Taylors series,
\$latex
sin x = +frac {x}{1!} – frac {x^3}{3!} + frac {x^5}{5!} – frac {x^7}{7!} +…
&s=2\$

\$latex
frac {sin x}{x} = 1 – frac {x^2}{3!} + frac {x^4}{5!} –…

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## Author: tomcircle

Math amateur

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