Surveyors must have a thorough knowledge of algebra, basic calculus, geometry, and trigonometry. This formula links problems in trigonometry and algebra. Muslim mathematicians introduced Euclidean Geometry, Spherical trigonometry and Arabic numerals in China. The methods used made no explicit use of algebra, nor trigonometry. He studied political philosophy, classics, mathematics, trigonometry, chemistry and history. Lambert was the first to introduce hyperbolic functions into trigonometry. Similar triangles also provide the foundations for right triangle trigonometry. It was Leonhard Euler who fully incorporated complex numbers into trigonometry. He was one of the first mathematicians in China to work on spherical trigonometry. In spherical trigonometry, angles are defined between great circles. Al-Tusi was the first to write a work on trigonometry independently of astronomy. Wildberger states that there are five basic laws in rational trigonometry. Spherical trigonometry differs from ordinary trigonometry in many respects. A common use of mnemonics is to remember facts and relationships in trigonometry. Angles are not used, and no trigonometry is involved.