## Mathematicians Of The Day

### 5th May

On this day in 1777, Leonhard Euler was the first to use the symbol

See THIS LINK.

*i*for $\sqrt{-1}$ in the paper*De Formulis Differentialibus Angularibus maxime irrationalibus quas tamen per logarithmos et arcus circulares integrare licet*[Of the most irrational Angular Differential Formulas, which, however, may be integrated by means of logarithms and circular arcs], presented to the St Petersburg Academy:-Quoniam mihi quidem alia adhuc via non patet istud praestandi nisi per imaginaria procedendo, formulam $\sqrt{-1}$ littera i in posterum designabo, ita ut sit i i = -1 ideoque 1/i = -i.[Since there is still no other way clear to me of accomplishing this except by an imaginary procedure, I will denote the formula $\sqrt{-1}$ by the letter

*i*in the future, so that*i i*= -1 and therefore 1/*i*= -*i*.]See THIS LINK.

Click on Ⓟ for a poster.

##### Born:

- 1580: Johann Faulhaber Ⓟ
- 1833: Lazarus Fuchs Ⓟ
- 1860: Charles Chree Ⓟ
- 1877: Alexander Brown
- 1883: Anna Johnson Wheeler Ⓟ
- 1889: René Eugène Gateaux Ⓟ
- 1895: Stefan Bergman Ⓟ
- 1897: Francesco Tricomi Ⓟ
- 1904: Alston Householder Ⓟ
- 1905: Margaret E Boyle Ⓟ
- 1923: Cathleen Morawetz Ⓟ

##### Died:

- 1859: Lejeune Dirichlet Ⓟ
- 1901: Georg Zehfuss Ⓟ
- 1954: Ethel Elderton
- 1957: Leopold Löwenheim Ⓟ
- 1972: William Whyburn Ⓟ
- 1989: Stefan Warschawski Ⓟ
- 2002: Barry Johnson Ⓟ
- 2020: Sergei Ivanovich Adian Ⓟ

#### Quotation of the day

##### From Stefan Bergman

I like your result. Let's make it a joint paper and I'll write the next one.