The number whose exact roots cannot be found are called surds. A surd in which the whole of the rational number is under the radical sign and makes the radicand is called pure surd. A surd having a rational coefficient other than unity is called a mixed surd. The algebraic sum of two surds or a sum of two unlike terms Binomial surds. Trinomial surds are called the algebraic sum of three surds and a rational quantity or the sum of three unlike terms.