A term can be the product of a number and one or more variables or a single number, with no variable. The expression 21 + 7x2 – 25yz has three terms: 21, 7x2, and -25yz. The expression 9g + 16 + 3 + s has four terms: 9g, 16, 3, s. The coefficient is the number that is multiplied by the variable(s) in a single term. In the expression 21 + 7x2 – 25yz, x2 has a coefficient of 7 and yz has a coefficient of -25. A term without a coefficient, like s, has an understood coefficient of 1. Terms that do not contain any variable are constants. In the above expressions, 21, 16, and 3 are constants. Like terms are terms that have the same variables, raised to the same exponents. For example, 11ab and 22ab are like terms, but 11ab2 and 22ab are not. Likewise, 0.1c 99c are like terms, but 2c and 2d are not. 12 and -6 are like terms, because they are both constants. When solving expressions or equations, we must combine like terms. To do so, we add their coefficients and keep the variable. This works because of the distributive property of multiplication. 2y + 3x2 - 3y + 0.5x2 Can you see that both 2 and -3 are multiplied by y? This would make y(2 – 3) y(2-3) + x2(3 + 0.5) Y(-1) + x(3.5) -y + 3.5x2 We usually put the higher exponents first, so: 3.5x2 - y