+ Adding and Subtracting Rational Expressions: The addition and subtraction of fractions can be carried out only when their denominators are identical. To get a required denominator, we may build up the denominator of a fraction. We multiply the numerator and denominator of a fraction by the same number (not zero) to get an equivalent fraction. Definition: Addition and Subtraction of Rational Numbers If a/b and c/b are rational numbers, then and
+ Adding and Subtracting with Unlike Denominators For fractions with different denominators, we build up one or both denominators to make the denominators the equal. The least common denominator (LCD) is the smallest number that is a multiple of all of the denominators. Procedure: Finding the LCD 1.Factor each denominator completely. 2.Write a product using each factor that appears in a denominator. 3.For each factor, use the highest power of that factor that occurs in the denominators.