If $2^x = \sqrt[3]{32}$, then $x$ is equal to
Aptitude
Surds and Indices
Difficulty: Easy
Choose an option
-
A5
-
B3
-
C3/5
-
D5/3
Answer
Correct Answer: 5/3
Explanation
### Concept & Formula
This problem is a fundamental test of translating radical notation (roots) into fractional exponents. Once the root is a fraction, you simply express the internal number as a prime base to equate both sides.
The core conversion rule is:
$$\sqrt[n]{x^m} = x^{\frac{m}{n}}$$
### Step-by-Step Solution
* **Given:**
$$2^x = \sqrt[3]{32}$$
* **Calculation:**
First, evaluate the number inside the cube root. We need to express $32$ as a power of the base $2$.
We know that $2 \times 2 \times 2 \times 2 \times 2 = 32$.
Therefore, $32 = 2^5$.
Substitute this back into the radical expression:
$$2^x = \sqrt[3]{2^5}$$
Convert the cube root into a fractional exponent. A cube root corresponds to the denominator $3$ in a fractional power:
$$2^x = (2^5)^{\frac{1}{3}}$$
Multiply the exponents using the power of a power rule:
$$2^x = 2^{\frac{5}{3}}$$
Since the bases on both sides of the equation are now exactly $2$, we can drop the bases and directly equate the exponents:
$$x = \frac{5}{3}$$
### Exam Strategy & Shortcut
**Direct Translation:** Memorize the prime powers up to $2^6$ and $3^5$. As soon as you read $\sqrt[3]{32}$, you should mentally translate $32$ to $2^5$, and the cube root to a division by $3$ on the exponent, immediately yielding $\frac{5}{3}$. This is a 5-second mental math problem.
### Common Pitfall
A frequent trap is confusing the numerator and denominator when converting roots. Students sometimes mistakenly write $(2^5)^{\frac{1}{3}}$ as $2^{\frac{3}{5}}$, leading them to confidently pick the incorrect option (c). Remember: Power is on top, Root is on the bottom.
### Final Answer
**Therefore, the correct answer is 5/3.**