What is the smallest number by which 72 must be multiplied to make it ...
Prime factorising 72, we get, 72 = 2×2×2×3×3 We know, a perfect cube has multiples of 3 as powers of prime factors. Here, number of 2's is 3 and number of 3's is 2. So we need to multiply another 3 in the factorization to make 72 a perfect cube.
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Understanding Perfect Cubes
To determine the smallest number by which 72 must be multiplied to become a perfect cube, we first need to factorize 72 into its prime factors.
Prime Factorization of 72
- 72 can be expressed as:
- 72 = 2 × 36
- 36 = 2 × 18
- 18 = 2 × 9
- 9 = 3 × 3
- Thus, the complete factorization is:
- 72 = 2^3 × 3^2
Characteristics of Perfect Cubes
- A perfect cube is a number whose prime factors all have exponents that are multiples of 3.
- For example, in a perfect cube, the exponent of each prime factor should ideally be 0, 3, 6, 9, etc.
Analyzing the Factorization
- From the factorization of 72:
- The exponent of 2 is 3 (which is already a multiple of 3).
- The exponent of 3 is 2 (which is not a multiple of 3).
Finding the Required Multiplier
- To make 3^2 a multiple of 3, we need to increase the exponent from 2 to 3.
- Thus, we need one additional factor of 3.
Conclusion
- Therefore, the smallest number we must multiply 72 by is:
- 3 (which corresponds to option 'D').
In summary, multiplying 72 by 3 results in 216, which equals 6^3, confirming it is a perfect cube.