Abul Wáfa
Abul Wafa Muhammad Ibn Muhammad Ibn Yahya Ibn Ismail al-Buzjani (940 – 997 or 998) was a Persian mathematician and astronomer. He was born in Buzjan, Nishapur in Iran.
He devised a wall quadrant for the accurate astronomy measurement of the declination of stars. He also introduced the tangent function and improved methods of calculating trigonometric tables and developed novel ways of solving some problems of spherical triangles.
He established the relations:
- Sin(a+b) = Sin a Cos b + Cos a Sin b
- Cos2a = 1 – 2Sin2a
- Sin2a = 2 Sina Cosa
and dicovered the Sine formula for spherical geometry:
- SinA/Sina = SinB/Sinb = SinC/Sinc
In 959 A.D. he moved to Iraq. He studied mathematics and worked principally in the field of trigonometry. He wrote a number of books, most of which no longer exist. He also studied the movements of the moon and there is a crater called Abul Wáfa (crater) on the moon.