This post about solving a rational equation is #15 in a series of posts to help you prepare for the Advanced Algebra and Functions part of the Accuplacer test.
Solve this rational equation:
Assume x is not equal to -8 or 2/3.
What do we mean by rational? The root is ratio. A rational number is a number that can be expressed as quotient — a ratio — of two integers. A rational expression is a quotient — a ratio — of algebraic expressions. A rational equation is an equation comprised of rational expressions.
To get started solving this rational equation, multiply both sides by . That should give you:
Cancel the terms that show up in both numerator and denominator. That’s on the left and on the right. That leaves:
(Yes, I could have just said “cross multiply,” but I hate that expression. It’s a personal quirk.) Now we’re done with denominators.
Subtract from both sides, and then switch the sides.
[For more about factoring, see “How to Factor a Quadratic.”
Set each factor equal to 0:
Remember that division by zero yields something undefined, so an x-value that makes a denominator zero is not a valid answer. So you need to make sure that the x values you’ve found do not make one of the denominators in the original question zero. To find those values, set those denominators equal to zero:
Oh, look: Those are the values that the question says are excluded. The question is telling you that a solution that causes the denominator to be zero is not a valid solution. But today that is not your problem, because that’s not one of the answers we found. We found and . Interesting factoid: The official practice question on which this question is based stipulates that x is not equal to -3/2 and then offers -3/2 as an answer choice. If there’s a lesson in that, it may be that it’s a good idea to reread the question before you give your final answer.
To complete the check, substitute and into the original equation.
This question is similar to question number 15 in the sample questions for the Accuplacer Advanced Algebra and Functions test.