Combining like terms

Terms with the same letter part that differ only in their coefficients are called like terms, for example 2x²y and -7x²y; 3a² and 3a are not like terms. Combining like terms means replacing their algebraic sum with a single term: the coefficients are added and the letter part stays, i.e. 9a - 4a = (9 - 4)a = 5a. We first bring each term to standard form and then combine like terms; a polynomial with no like terms and with every term in standard form is said to be in standard form. Marking like terms with different underlines helps to avoid mistakes. The value of a simplified polynomial is much easier to find.