Problem 72 - Algebra 1

Question

Rewrite the expression using positive exponents. $$\frac{1}{4 x^{-7}}$$

Step-by-Step Solution

Answer

The expression written using positive exponents is \(\frac{1}{4x^7}\).

Step 1: Understand negative exponent rule

A negative exponent means to reciprocate the base. So, the rule for negative exponents is \(a^{-n} = \frac{1}{a^n}\) where a is the base and n is the negative exponent.

Step 2: Apply the rule to get rid of the negative exponent

Applying the rule to our term, \(x^{-7}\), it becomes \(\frac{1}{x^{7}}\).

Step 3: Rewrite the entire expression

The original expression was \(\frac{1}{4 x^{-7}}\). We substitute the result from step 2 into this, getting \(\frac{1}{4}\) times \(\frac{1}{x^{7}}\). This simplifies to \(\frac{1}{4x^7}\).

Key Concepts

Exponent Rules

Exponential expressions can seem daunting at first, but by understanding a few basic rules, they become manageable and can be easily simplified. One of the foundational exponent rules is dealing with negative exponents. The rule states that when a number is raised to a negative exponent, like \(a^{-n}\), it's equivalent to the reciprocal of that number raised to the positive exponent: \(a^{-n} = \frac{1}{a^n}\). This is also true for variables and algebraic expressions.

Other essential exponent rules include multiplying powers with the same base (add their exponents), dividing powers with the same base (subtract the exponents), and taking a power to a power (multiply the exponents). Understanding these rules allows students to manipulate and simplify algebraic expressions involving exponents with confidence.

Reciprocals in Algebra

Algebra often requires understanding reciprocals—particularly when dealing with negative exponents or division of algebraic fractions. A reciprocal literally 'flips' a fraction, turning \(\frac{a}{b}\) into \(\frac{b}{a}\), or in the case of a whole number or a variable, \(a\) would become \(\frac{1}{a}\). It is essentially exchanging the numerator and denominator's positions.

Reciprocals are especially important because they are the key to removing negative exponents. For instance, \(x^{-7}\) can be rewritten as the reciprocal of \(x\) to the seventh power, or \(\frac{1}{x^7}\). Reciprocals also play a significant role when dividing fractions or rational expressions, as multiplying by the reciprocal is the method used to perform the division.

Simplifying Algebraic Expressions

Simplification is the process of reducing complexity in an algebraic expression to make it easier to understand or solve. This often includes combining like terms, factoring, expanding expressions, and simplifying fractions. For expressions with exponents, applying exponent rules systematically contributes significantly to the simplification process.

When simplifying an expression like \(\frac{1}{4x^{-7}}\), the goal is to apply these rules to eliminate negative exponents and simplify the fraction. In this case, the negative exponent is addressed by recognizing that \(x^{-7}\) is the reciprocal of \(x^7\), and thus the expression simplifies to \(\frac{1}{4x^7}\), where all exponents are now positive. This cleans up the expression and makes it easier to further manipulate or use within equations.