865?-922?

Persian mathematician and astronomer who wrote a commentary on Euclid's Elements and made early use of the trigonometric tangent function. Little is known of al-Nayrizi's life, but his name suggests that he came from the town of Nayriz in what is now central Iran and he probably served the Abbasid caliphs in Baghdad. In addition to his writings on Euclid and Ptolemy's Almagest and Tetrabiblos, al-Nayrizi discussed the problem of calculating the exact direction of Mecca, an important part of the Muslim daily prayer ritual. In so doing, he used the tangent function, though he was not the first to develop that concept.