Chapter 2: Problem 21
In \(13-24,\) divide and express each quotient in simplest form. In each case, list any values of the variables for which the fractions are not defined. $$ \frac{4 b+12}{b} \div(b+3) $$
Short Answer
Expert verified
The simplified form is \(\frac{4}{b}\), undefined for \(b=0\) and \(b=-3\).
Step by step solution
01
Write the Expression as a Fraction Division
The given expression is presented as one fraction divided by another expression. Write it as a fraction division:\[ \frac{4b+12}{b} \div (b+3) \]
02
Rewrite as Multiplication of Reciprocal
To divide by a fraction or expression, multiply by its reciprocal. The reciprocal of \((b+3)\) is \(\frac{1}{b+3}\). Rewrite the expression as:\[ \frac{4b+12}{b} \times \frac{1}{b+3} \]
03
Simplify the Fraction
First, factor the numerator of the first fraction. The expression \(4b+12\) can be factored as \(4(b+3)\). So the fraction becomes:\[ \frac{4(b+3)}{b} \times \frac{1}{b+3} \]
04
Cancel Common Factors
Notice that \((b+3)\) appears in both the numerator and the denominator. Cancel these terms from both the fractions:\[ \frac{4 \cancel{(b+3)}}{b} \times \frac{1}{\cancel{(b+3)}} = \frac{4}{b} \cdot 1 = \frac{4}{b} \]
05
Identify Restrictions on the Variable
The original expression contains two denominators, \(b\) and \((b+3)\). Thus, \(b\) cannot be zero and \(b\) cannot be -3, as these would make the original expression undefined.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Division of Fractions
Understanding how to divide fractions is a fundamental skill in algebra, and it applies to rational expressions as well. When you see a division sign between two fractions or expressions, think of it as a multiplication problem. This is because dividing by a fraction is the same as multiplying by its reciprocal.
- The reciprocal of a number is simply flipping the numerator and the denominator. For example, the reciprocal of \(a/b\) is \(b/a\).
- In our case, we turn \(\frac{4b+12}{b} \, \div \, (b+3)\) into \(\frac{4b+12}{b} \, \times \, \frac{1}{b+3}\).
- This changing from division to multiplication allows us to more easily simplify the expression.
Factoring Polynomials
Factoring is an essential tool in simplifying rational expressions. It involves breaking down a polynomial into simpler parts, or factors, that when multiplied together give you the original polynomial.
- In our exercise, we need to factor the numerator \(4b+12\).
- This can be rewritten as \(4(b+3)\). We factored out the common factor '4'.
- Once we've factored, the expression becomes \(\frac{4(b+3)}{b}\).
Undefined Expressions
In mathematics, an undefined expression is one in which the operations can't be performed because they break mathematical rules. These occur typically when a denominator equals zero.
- In the expression \(\frac{4}{b}\), it's undefined when \(b = 0\), because division by zero is not permitted.
- Similarly, in the original expression \(b+3\) in the denominator also cannot be zero. Thus, \(b = -3\) would make it undefined.
Simplifying Expressions
Once you've performed division and factoring, the next logical step is simplification. This involves reducing the expression to its simplest form.
- With our expression, after multiplying and factoring, we ended with \(\frac{4\cancel{(b+3)}}{b} \times \frac{1}{\cancel{(b+3)}} = \frac{4}{b}\).
- The simplification occurs by cancelling like terms, such as \(b+3\) in the numerator and denominator.
- This leaves us with a cleaner and simpler expression that is more manageable.