*Aliboran (El Biruni, 973-1048), is one of the Turkish-Islamic scientists who is the cornerstone of development of science and mathematics; he has been described as “One of the most brilliant mind of all times”. Biruni is accepted as the pioneer of “Scientific observation” and many mathematical fields such as, “Trigonometry”, “Projection Geometry”; despite the fact that he wrote his works in Arabic that was accepted as the scientific language in his time, he also took notes in Turkish from time to time. In this study, Biruni’s studies on mathematics are briefly summarized. Mainly, proof of two of his theorems, which were expressed by making attributions to him in some Biruni investigations, are given whose proofs were not given (probably because they couldn’t be found). These proofs, which were, we guess, commented orally by Biruni, are verified by using modern mathematical notations and terms. *

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