# Ex 7.1, 2 - Chapter 7 Class 8 Cubes and Cube Roots

Last updated at Aug. 1, 2018 by Teachoo

Last updated at Aug. 1, 2018 by Teachoo

Transcript

Ex 7.1, 2Find the smallest number by which each of the following numbers must be multiplied to obtain a perfect cube.(i) 243 We see that 243 = 3 × 3 × 3 × 3 × 3 Since 3 does not occur in triplets, ∴ 243 is not a perfect cube. So, we multiply by 3 to make triplet So, our number becomes 243 × 3 = 3 × 3 × 3 × 3 × 3 × 3 Now, it becomes a perfect cube. So, we multiply 243 by 3 to make it a perfect cube Ex 7.1, 2Find the smallest number by which each of the following numbers must be multiplied to obtain a perfect cube.(ii) 256 We see that 256 = 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2 Since 2 does not occur in triplets, ∴ 256 is not a perfect cube. So, we multiply by 2 to make triplet So, our number becomes 256 × 2 = 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2 Now, it becomes a perfect cube. So, we multiply 256 by 2 to make it a perfect cube Ex 7.1, 2Find the smallest number by which each of the following numbers must be multiplied to obtain a perfect cube.(iii) 72 We see that 72 = 2 × 2 × 2 × 3 × 3 Since 3 does not occur in triplets, ∴ 72 is not a perfect cube. So, we multiply by 3 to make triplet So, our number becomes 72 × 3 = 2 × 2 × 2 × 3 × 3 × 3 Now, it becomes a perfect cube. So, we multiply 72 by 3 to make it a perfect cube Ex 7.1, 2Find the smallest number by which each of the following numbers must be multiplied to obtain a perfect cube.(iv) 675 We see that 675 = 3 × 3 × 3 × 5 × 5 Since 5 does not occur in triplets, ∴ 675 is not a perfect cube. So, we multiply by 5 to make triplet So, our number becomes 675 × 5 = 3 × 3 × 3 × 5 × 5 × 5 Now, it becomes a perfect cube. So, we multiply 675 by 5 to make it a perfect cube Ex 7.1, 2Find the smallest number by which each of the following numbers must be multiplied to obtain a perfect cube.(v) 100 We see that 100 = 2 × 2 × 5 × 5 Since 2 & 5 does not occur in triplets, ∴ 100 is not a perfect cube. So, we multiply by 2 × 5 to make triplet So, our number becomes 100 × 2 × 5 = 2 × 2 × 5 × 5 × 2 × 5 = 2 × 2 × 2 × 5 × 5 × 5 Now, it becomes a perfect cube. So, we multiply 100 by 2 × 5 i.e. 10 to make it a perfect cube

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Davneet Singh

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 8 years. He provides courses for Maths and Science at Teachoo. You can check his NCERT Solutions from Class 6 to 12.