## Mathematicians Of The Day

### 6th July

On this day in 1708, de Moivre wrote to Johann Bernoulli about Machin's series: $(\frac{16}{5} - \frac{4}{239}) - \frac{1}{3} (\frac{16}{5^3} - \frac{4}{239^3}) + \frac{1}{5} (\frac{16}{5^5} - \frac{4}{239^5})\, ... = 3.14159 ... = \pi$, on this occasion giving two different proofs that it converges to π.

This series follows from the identity $\frac {\pi }{4}=4\tan^{-1} {\frac {1}{5}}-\tan^{-1} {\frac {1}{239}}$.

The postage stamp of one of today's mathematicians at THIS LINK was issued in 2017.

This series follows from the identity $\frac {\pi }{4}=4\tan^{-1} {\frac {1}{5}}-\tan^{-1} {\frac {1}{239}}$.

The postage stamp of one of today's mathematicians at THIS LINK was issued in 2017.

Click on Ⓟ for a poster.

##### Born:

- 1849: Alfred Kempe Ⓟ
- 1904: Alexander Buchan
- 1910: Lothar Collatz Ⓟ
- 1917: Henry Jack Ⓟ
- 1928: Bernard Malgrange Ⓟ
- 1929: Jock Hoe Ⓟ
- 1945: Leon Simon Ⓟ

##### Died:

- 1476: Regiomontanus Ⓟ
- 1854: Georg Simon Ohm Ⓟ
- 1959: Agnes Wells Ⓟ
- 2013: Ismail Mohamed Ⓟ
- 2020: Ronald Graham Ⓟ

#### Quotation of the day

##### From Ronald Graham

Well, as you know, there are 24 hours in every day. And if that's not enough, you've always got the nights!