Who among the following found a formula for "infinite series for pi"?

The correct answer is Option (3) → Srinivasa Ramanujan

The Indian mathematician Srinivasa Ramanujan (1887–1920) published, in 1914, a set of infinite series for \(\frac{1}{\pi}\) that give many correct digits of \(\pi\) from only a few terms. Series built on his are still used by computers to calculate \(\pi\) to billions of digits. His birthday, 22 December, is observed as National Mathematics Day.