In the year 949 AD, the mathematicians Abu Sahl Wayjan ibn Rustam al Quhi and Mohammad Abu'l-Wafa al'Buzjani were both nine years old.  Al-Quhi was famous for his work in astronomy and geometry.  In 969 and 970 Al-Quhi observed the summer and winter solstices.   He built an observatory in 988, but it was closed after one year.  Al-Quhi mostly studied geometry and its relation to cubic and quartic equations.  He died in Persia around 1000 AD.
 
Abu’l Wafa also had an interest in astronomy and this led to his study of trigonometry. In his study of the orbit of the moon, Abu’l Wafa was the first to use tangent function and he used a new method to construct sine and tangent tables.  His tables were accurate to eight decimal places, an improvement upon Ptolemy’s tables which were only accurate to three decimal places.  Abu’l Wafa is also credited with the discovery of the secant and cosecant functions and he studied the relations between the six trigonometric functions.  In addition to his work in trigonometry, Abu’l Wafa wrote commentaries and translated the works of Diophantus, Euclid, and al'Khwarizmi. He is also responsible for introducing the idea of a “rusty compass,” or a compass which can be held at a fixed length.  Abu’l Wafa died in 998, two years before Al-Quhi.

Author: Tim Lucas

References:
MacTutor History of Mathematics Archive
http://www-history.mcs.st-andrews.ac.uk/history/Mathematicians/Quhi.html
http://www-history.mcs.st-andrews.ac.uk/history/Mathematicians/Abu'l-Wafa.html

Eves, Howard.  An Introduction to the History of Mathematics,  Philadelphia:  Saunders
College Publishing, 1990.