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DemingEarly College High SchoolUnit 3.0 Advanced Algebra and Functions (AAF) 3.3 Radical and Rational Equations
Unit 3.0 Advanced Algebra and Functions (AAF)3.3 Radical and Rational Equations 3.3.1 Rational Expressions A rational expression is a fraction where the numerator and denominator are both polynomials. Some examples of rational expressions include the following: , , and . Since these refer to expressions and not equations, they can be simplified but not solved. Using the rules in the previous Exponents and Root sections, some rational expressions with monomials can be simplified. Other rational expressions such as the last example, , take more steps to be simplified. First the polynomial on top can be factored into . Then the common factors can be canceled and the expression can be simplified to .
Unit 3.0 Advanced Algebra and Functions (AAF)3.3 Radical and Rational Equations 3.3.1 Rational Expressions Consider this problem as an example of using rational expressions. Donte wants to lay sod in his rectangular backyard. The length of the yard is given by the expression and the width is unknown. The area of the yard is . Donte needs to find the width of the yard. Knowing that the area of a rectangle is length multiplied by width, an expression can be written to find the width: , area divided by length. Simplifying this expression by factoring out 10 on the top and 2 on the bottom leads to this expression: . By canceling out the , that results in . The width of the yard is 5 by simplifying a rational expression.
Unit 3.0 Advanced Algebra and Functions (AAF)3.3 Radical and Rational Equations 3.3.2 Rational Equations A rational equation can be as simple as an equation with a ratio of polynomials, , set equal to a value, where and are both polynomials. Notice that a rational equation has an equal sign, which is different from expressions. This leads to solutions, or numbers that make the equation true. It is possible to solve rational equations by trying to get all of the x terms out of the denominator and then isolate them on one side of the equation. For example, to solve the equation, , start by multiplying both sides by (). This will cancel on the left side leaving then . Now, subtract from both sides, which yields , so .
Unit 3.0 Advanced Algebra and Functions (AAF)3.3 Radical and Rational Equations 3.3.2 Rational Equations Sometimes, when solving rational equations, it can be easier to try to simplify the rational expression by factoring the numerator and denominator first, then cancelling out common factors. For example, to solve: . Start by factoring the numerator: . Then factor the numerator into . The ’s cancel out leaving . Now the same method can be followed. Multiplying both sides by and performing the multiplication on the left yields , which can be simplified to .
Unit 3.0 Advanced Algebra and Functions (AAF)3.3 Radical and Rational Equations 3.3.3 Rational Functions A rational function is similar to a rational equation, but it includes two variables. In general, a rational function is in the form: , where and are polynomials. Rational functions are defined everywhere except where the denominator is equal to zero. When the denominator equal to zero, this indicates a “hole” in the graph or an asymptote. An asymptote can be either vertical, horizontal, or slant. A hole occurs when both the numerator and denominator are equal to 0 for a given value of x. An asymptote can have at most one vertical, one horizontal, or one slant asymptote. An asymptote is a line such that the distance between the curve and the line tends toward 0, but never reaches it, as the line heads toward infinity.
Unit 3.0 Advanced Algebra and Functions (AAF)3.3 Radical and Rational Equations 3.3.3 Rational Functions Examples of these types of functions are shown here and the next page. The first graph shows a rational function with a vertical asymptote at x = 0. This can be found by setting the denominator equal to 0. In this case, it is just x = 0.
Unit 3.0 Advanced Algebra and Functions (AAF)3.3 Radical and Rational Equations 3.3.3 Rational Functions The second graph shows a rational function with a vertical asymptote at x = -0.5. Again this can be found by setting the denominator equal to 0 and solving for x. So: → → → .