A term is a part of an expression that is connected to another term by a - or a - sign. For example, in the expression \( 4 x+6 y-9 z \), the terms are \( 4 x, 6 y \) and \( 9 z \). If there is no sign witten in front of a tom, it is alvays understood theat the sign is + . A (numerical) coefficlent is a factor by which the rest of a term is multipled. For example, the term \( 5 x y \) has a coefficient of 5 and the term \( -15 z \) has a coelficient of -15 . The degree of an expression is the highest exponent (or power) of any variable contained in the expression. For example, the expression \( 3 x+7 \) is a linear (or first degree) Expression, \( 9 x^{2}-4 x+1 \) is quadratic (or second degree) and \( 10 y^{3}+4 y^{2}-y+8 \) is cublic (or third degree). A linear equalion is therefore ono in which the largest value of the exponents is 1 . In an expression, terms that differ only in their coofficients are said to be like terms. For example, in the expression \( 15 x-5 y+32-4 x+6 x y+x^{2}+3 y \), the terms \( 15 x \) and \( -4 x \) are like terms. Also, th terms \( -5 y \) and \( +3 y \) are like terms. An equation is a statement that two expressions are equal. The two expressions are shown to be equal by m of an equals \( (=) \) sign. Example: Suppose that the two expressions \( 3 x+6 \) and \( 5 x-2 \) are equal. The resulting equation is: