 In most cases, the best that can be done is computing approximate values of the roots with a root-finding algorithm.The systematic use of algebraic manipulations for simplifying expressions (more specifically equations)) may be dated to 9th century, with al-Khwarizmi's book "The Compendious Book on Calculation by Completion and Balancing", which is titled with two such types of manipulation.However, even for solving quadratic equations, factoring method was not used before Harriot’s work published in 1631, ten years after his death.