Question 117·Hard·Equivalent Expressions
If and are positive real numbers, which of the following is equivalent to
For expression-equivalence questions with radicals and powers, first convert all roots into fractional exponents so everything is in the form . Then treat each base separately: when multiplying, add exponents; when dividing, subtract denominator exponents from numerator exponents; and when raising a power to a power, multiply exponents. Carefully track signs and fractions, especially with negative exponents, and only at the end match your simplified and exponents to the choices.
Hints
Turn radicals into exponents
Rewrite the cube root and square root using fractional exponents. Remember, the nth root of can be written as .
Handle the division first
Focus on the part where one expression is divided by another. For each base ( and ), subtract the exponent in the denominator from the exponent in the numerator.
Deal with the negative power
For , use the rule on each factor separately, then combine the exponents of and from all parts of the expression.
Desmos Guide
Assign values to p and q
Choose convenient positive values for and , such as and . In Desmos, type p = 4 and q = 9 on separate lines so Desmos treats them as constants.
Enter the original expression
On a new line, type the original expression using exponents: for example, (p^5*q)^(1/3) / sqrt(p*q^3) * (p^(1/2)*q^(-4/3))^(-2). Desmos will show a numeric value for this line.
Test each answer choice
For each choice A–D, type a new line with its expression exactly as written in the problem (using the same and ). Compare the numeric outputs: the choice whose value matches the original expression for this set of and (and, if you like, for a second set such as , ) is the equivalent expression.
Step-by-step Explanation
Rewrite radicals using rational exponents
Use the rule that the nth root of is . Rewrite the cube root as and the square root as . So the whole expression becomes divided by , multiplied by . In other words, it is times .
Simplify the fraction part by subtracting exponents
Now simplify the fraction by subtracting exponents for like bases (numerator minus denominator). For , compute . With common denominator 6, this is , so the exponent on is . For , compute . With denominator 6, this is , so the exponent on is . After this step, the expression is .
Apply the power-of-a-power rule
Use the rule on . For , multiply exponents: , so you get . For , multiply exponents: , so you get . So simplifies to , and the whole expression is now .
Combine like bases to get the final exponents
Combine the terms and the terms by adding their exponents. For , add and : , so the overall exponent on is . For , add and . Rewrite as , so , so the overall exponent on is . Therefore, the entire expression simplifies to , which matches answer choice A.