Person: AlSijzi, Abu Said Ahmad ibn Muhammad
AlSijzi was an Islamic astronomer and mathematician who wrote on the geometry of spheres.
Mathematical Profile (Excerpt):
 It is quite possible that 'Adud adDawlah was alSijzi's patron since he was a leader well known for patronising the arts and science.
 We also know that alSijzi worked in Shiraz making astronomical observations during 969970.
 We mentioned above that alSijzi corresponded with alBiruni.
 AlSijzi's mathematical papers are less numerous but more significant than his astrological ones, and he is therefore better known as a geometer.
 Among the problems alSijzi discusses are the following.
 A treatise on spheres by alSijzi Book of the measurement of spheres by spheres is of considerable interest.
 The treatise, dated by alSijzi 969, contains twelve theorems investigating a large sphere containing between one and three smaller spheres.
 AlSijzi finds the volume inside the large sphere which is outside the small ones inside it.
 is due to an oversight made by AlSijzi, who does not use fourdimensional spheres anywhere else in his treatise.
 We note that the treatise was written around 969 AD, at a time when alSijzi was a very young and perhaps inexperienced geometer.
 Another short work by alSijzi is the Treatise on how to imagine the two lines which approach but do not meet when they are produced indefinitely, which the excellent Apollonius mentioned in the second Book of the Conics.
 This is considered by most historians to be a threedimensional extension by alSijzi of the geometrical algebra propositions in Book 2 of Euclid's Elements.
Born about 945, Sijistan, Persia (now Iran). Died about 1020.
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Tags relevant for this person:
Ancient Arab, Astronomy, Origin Iran, Special Numbers And Numerals
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Epochs: 1
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References
Adapted from other CC BYSA 4.0 Sources:
 Oâ€™Connor, John J; Robertson, Edmund F: MacTutor History of Mathematics Archive