Polynomials
An algebraic sum of several monomials is called a polynomial, and the monomials forming it are the terms of the polynomial. A polynomial of two terms is a binomial and one of three terms is a trinomial; for example a² - 4b is a binomial and x³ - 2xy + 5y² is a trinomial. Because subtraction is the same as adding the opposite, a minus sign belongs to the term that follows it: the terms of 2a²b - 5ab + 7b² - 1 are 2a²b, -5ab, 7b² and -1. A monomial is also considered a polynomial (it has one term). Polynomials often appear in geometry: if a small square of side c is cut out of a square of side a, the remaining area is the binomial a² - c². To find the value of a polynomial we substitute numbers for the letters and carry out the operations in order.
“Term counting”: a long polynomial is written on the board. Pupils take turns pointing at one term and reading it with its sign. At the end the number of terms is counted and the polynomial is named (binomial, trinomial).