Find cube roots by grouping prime factors in threes.
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A cube root undoes cubing; find it with prime factors.
We know that . Here, 8 is the perfect cube, and 2 is the cube root of 8. Finding a cube root is simply the inverse operation of finding a cube.
The cube root symbol, and how to write it.
Worked example: the cube root of 3375.
Problem. Determine if 3375 is a perfect cube. If it is, find its cube root.
Worked example: is 500 a perfect cube?
Problem. Check if the number 500 is a perfect cube using prime factorisation.
Group prime factors in threes to find the cube root.
To find the cube root of a number, we can use prime factorisation and group the identical factors. Let us examine the prime factorisation of to find its cube root. First, we break down into its prime factors, resulting in . Next, we must organise these prime factors into identical groups to determine if it is a perfect cube. Writing this with exponents, we get , which shows each prime factor appears the correct number of times. By taking one number from each triplet, the cube root calculation becomes . Multiplying these factors together, we conclude that the cube root of is .
Match each cube to its prime factors.
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Find the number to multiply by to make a perfect cube.
What number will you multiply by 1323 to make it a perfect cube? Use the step-by-step fields below to show your prime factorization process.
Identify the number you are starting with.
What method will you use to determine the missing factors?
Write out the prime factorization of 1323.
Which prime factor does not form a complete triplet?
What is the smallest number to multiply by?
Check your work: does multiplying give a perfect cube?