The cube root of 5 is , and because 5 is prime, the radical does not simplify.
Quick Answer:
Result:
Notation: or
Method shown: estimation between neighbouring cubes
Approximate value: (to 3 decimal places, irrational)
Exact form: (already in simplest radical form)
Quick Reference Table
Number | Simplified cube root | Decimal (3 dp) |
|---|---|---|
Where the Cube Root of 5 Appears
The cube root of 5 is the edge length of a cube whose volume is 5 cubic units. It also appears in scaling problems: a cube-shaped container whose capacity must grow five times, while staying a cube, needs each edge multiplied by , not by 5.
What Is the Cube Root of 5?
The cube root of a number is the value that, multiplied by itself three times, returns that number. Since no whole number cubed equals 5, the cube root of 5 sits between and .
The result is an irrational number that never terminates and never repeats. Because 5 is prime, it carries no perfect-cube factor, so is already in its simplest form, the same principle at work across cube numbers and radicals.
How to Find the Cube Root of 5 (Methods)
Method 1: Estimation between neighbouring cubes
Locate 5 between the two nearest perfect cubes.
So lies between 1 and 2. Since 5 is roughly midway, start near the middle. Testing :
That is below 5, so try :
That is just above 5, so the answer sits between 1.70 and 1.72. Testing :
Final answer: to three decimal places.
Method 2: Why it will not simplify
Write 5 in terms of its prime factors.
For a factor to leave a cube root, it must appear three times. The single 5 has no group of three.
Final answer: is already in simplest radical form.
Common Mistakes With Cube Root of 5
Mistake 1: Dropping the cube-root index
Where it slips in: writing the radical quickly.
Don't do this: writing when you mean the cube root.
The correct way: always show the index: . Without the little 3 it reads as a square root, giving instead of .
Mistake 2: Trying to simplify a prime radical
Where it slips in: assuming every cube root breaks down like .
Don't do this: writing as a product of smaller radicals.
The correct way: a prime number under a cube root has no perfect-cube factor, so it stays as .
Mistake 3: Guessing the value is close to 2
Where it slips in: noticing 5 is near 8 and assuming the cube root is near 2.
Don't do this: answering roughly 1.9 or 2.
The correct way: cube roots grow slowly. Since , the answer is close to 1.71, not 2.
To build cube-root fluency with a teacher, explore Bhanzu's algebra tutor or math classes online.
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