Which of the following numbers are not perfect cubes?
(i) 216 (ii) 128
(iii) 1000 (iv) 100
(v) 46656
(i) Prime factorization of 216:
216 = 2 × 2 × 2 × 3 × 3 × 3 = 23 × 33
Here we can see that each prime factor is appearing as many times as a perfect multiple of 3, hence, 216 is a perfect cube.
(ii)The prime factorization of 128 is:
128 = 2 × 2 × 2 × 2 × 2 × 2 × 2
Here, we can observe that each prime factor is not appearing as many times as a perfect multiple of 3.
One 2 is remaining after grouping the triplets of 2 Hence, 128 is not a perfect cube.
(iii) The prime factorization of 1000 is:
1000 = 2 × 2 × 2 × 5 × 5 × 5
Here, we can observe that each prime factor is appearing as many times as a perfect multiple of 3.
Hence, 1000 is a perfect cube
(iv)The prime factorization of 100 is:
100 = 2 × 2 × 5 × 5
Here, we can see that every prime factor is not appearing as many times as a perfect multiple of 3.
Two 2s and two 5s are remaining if we group the triplets.
Therefore, 100 is not a perfect cube
(v)The prime factorization of 46656 is:
46656 = 2 × 2 × 2 × 2 × 2 × 2 × 3 × 3 × 3 × 3 × 3 × 3
Here, we can see that number of 2s and 3s is 6 each and we know that 6 is divisible by 3.
Hence, 46656 is a perfect cube