Remember how to do this? Since the denominators are 6, 10, and 4, you want to find the least common denominator and express each fraction with this denominator before adding. BTW, you can add fractions by finding any common denominator; it does not have to be the least.

You focus on using the least because then there is less simplifying to do. But either way works.

### Example Questions

Finding the least common denominator is the same as finding the least common multiple of 4, 6, and There are a couple of ways to do this. The first is to list the multiples of each number and determine which multiples they have in common. The least of these numbers will be the least common denominator. The other method is to use prime factorization , the process of finding the prime factors of a number.

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This is how the method works with numbers. The LCM will contain factors of 2, 3, and 5. Multiply each number the maximum number of times it appears in a single factorization. In this case, 3 appears once, 5 appears once, and 2 is used twice because it appears twice in the prime factorization of 4. Now that you have found the least common multiple, you can use that number as the least common denominator of the fractions.

Multiply each fraction by the fractional form of 1 that will produce a denominator of In the next example, we show how to find the least common multiple of a rational expression with a monomial in the denominator. Find the least common multiple. Both 5 and 7 appear at most once. For the variables, the most m appears is twice. Compare each original denominator and the new common denominator. Remember that m cannot be 0 because the denominators would be 0.

If possible, simplify by finding common factors in the numerator and denominator. This rational expression is already in simplest form because the numerator and denominator have no factors in common. That took a while, but you got through it.

### Most Used Actions

Adding rational expressions can be a lengthy process, but taken one step at a time, it can be done. Find the prime factorization of each denominator.

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In this case, it is easier to leave the common multiple in terms of the factors, so you will not multiply it out. Subtract the numerators and simplify. Otherwise you would be subtracting just the t. The video that follows contains an example of adding rational expressions whose denominators are not alike. The denominators of both expressions contain only monomials.

The video that follows contains an example of subtracting rational expressions whose denominators are not alike. The denominators are a trinomial and a binomial. In the next example, we show how to find a common denominator when there are no common factors in the expressions. Because they have no common factors, the least common multiple, which will become the least common denominator, is the product of these denominators.

Then rewrite the subtraction problem with the common denominator. It makes sense to keep the denominator in factored form in order to check for common factors. In the video that follows, we present an example of adding two rational expression whose denominators are binomials with no common factors. You may need to combine more than two rational expressions.

## Multiplication of Rational Numbers

While this may seem pretty straightforward if they all have the same denominator, what happens if they do not? In the example below, notice how a common denominator is found for three rational expressions. Once that is done, the addition and subtraction of the terms looks the same as earlier, when you were only dealing with two terms.

Find the least common multiple by factoring each denominator. Multiply each factor the maximum number of times it appears in a single factorization. Rewrite the original problem with the common denominator. Check for simplest form. In the video that follows we present an example of subtracting 3 rational expressions with unlike denominators. One of the terms being subtracted is a number, so the denominator is 1.

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The LCM becomes the common denominator. Multiply each expression by the equivalent of 1 that will give it the common denominator.

## Rational Expressions- Definition and Simplification with Examples

The domain is found by setting the denominators equal to zero. In this last video, we present another example of adding and subtracting three rational expressions with unlike denominators. In the next sections we will introduce some techniques for solving rational equations. The methods shown here will help you when you are solving rational equations. To add and subtract rational expressions that share common factors, you first identify which factors are missing from each expression, and build the LCD with them.

To add and subtract rational expressions with no common factors, the LCD will be the product of all the factors of the denominators. Rational expressions are multiplied and divided the same way as numeric fractions.

To multiply, first find the greatest common factors of the numerator and denominator. Next, regroup the factors to make fractions equivalent to one. Then, multiply any remaining factors. To divide, first rewrite the division as multiplication by the reciprocal of the denominator.

## SAT Math : How to multiply rational expressions

The steps are then the same as for multiplication. When expressing a product or quotient, it is important to state the excluded values.

These are all values of a variable that would make a denominator equal zero at any step in the calculations. Skip to main content. Module 7: Rational Expressions and Equations. Search for:. Operations on Rational Expressions Learning Outcomes Multiply and divide rational expressions Add and subtract rational expressions Add and subtract rational expressions with like denominators Add and subtract rational expressions with unlike denominators using a greatest common denominator Add and subtract rational expressions that share no common factors Add and subtract more than two rational expressions.

Multiply and Divide. Example Multiply. Show Solution Multiply the numerators, and then multiply the denominators. When multiplying rational expressions, it is equally helpful to factor the numerators and denominators before multiplying. This expression is very simple and there is no factoring that can be done prior to multiplying, so we multiply immediately. Note that could multiply the factors after simplifying, but this really depends on what we plan on doing with the expression after simplifying.