1. Which of the following numbers are not perfect cubes?
216
(ii 128
(iv) 100
(v) 46656
2. Find the smallest number by which each of the following numbers must be multiplied
to obtain a perfect cube.
@ 243
() 256
Gji) 72
(iv) 675
(v) .100
3. Find the smallest number by which each of the following numbers must be divided to
obtain a perfect cube.
81
(ii) 128
(ii) 135
(iv) 192
(v) 704 x
Parikshit makes a cuboid of plasticine of sides 5cm, 2 cm, 5 cm. How many such
cuboids will he need to form a cube?
7.3 Cube Roots
Answers
Answer:
1. (I)216 is a perfect cube
(ii)128 is not a perfect cube
(iii)100 is not a perfect cube
(iv)46656 is a perfect cube
2. (I) 3 is the smallest required number to make 243 obtain a perfect cube
(ii) 2 is the smallest required number to make 256 obtain a perfect cube
(iii) 3 is the smallest required number to make 72 obtain a perfect cube
(iv) 5 is the smallest required number to make 675 obtain a perfect cube
(v) 10 is the smallest required number to make 100 obtain a perfect cube
4. Volume of cuboid is 5*2*5 is equal to 2*5*5 cm3
To make it a cube need to make this a pefect cube number.
So we need 2*5*5 cuboids
or 20 cuboids.
Explanation:
1. (I)We have 216 - 2*2*2*3*3*3
Grouping the prime factors of 216 into triples no factor is leftover.
(ii) We have 128 - 2*2*2*2*2*2*2
Grouping the prime factors of 128 into triples one factor is leftover.
(iii) We have 100 - 2*2*5*5
Grouping the prime factors of 100 into triples we doesn't get any triples. Factors 2*2 and 5*5 are not in triples.
(iv) We have 46656 - 2*2*2*2*2*2*3*3*3*3*3*3
Grouping the prime factors of 46656 into triples no factor is leftover.
Answer:
Answer:
1. (I)216 is a perfect cube
(ii)128 is not a perfect cube
(iii)100 is not a perfect cube
(iv)46656 is a perfect cube
2. (I) 3 is the smallest required number to make 243 obtain a perfect cube
(ii) 2 is the smallest required number to make 256 obtain a perfect cube
(iii) 3 is the smallest required number to make 72 obtain a perfect cube
(iv) 5 is the smallest required number to make 675 obtain a perfect cube
(v) 10 is the smallest required number to make 100 obtain a perfect cube
4. Volume of cuboid is 5*2*5 is equal to 2*5*5 cm3
To make it a cube need to make this a pefect cube number.
So we need 2*5*5 cuboids
or 20 cuboids.
Explanation:
1. (I)We have 216 - 2*2*2*3*3*3
Grouping the prime factors of 216 into triples no factor is leftover.
(ii) We have 128 - 2*2*2*2*2*2*2
Grouping the prime factors of 128 into triples one factor is leftover.
(iii) We have 100 - 2*2*5*5
Grouping the prime factors of 100 into triples we doesn't get any triples. Factors 2*2 and 5*5 are not in triples.
(iv) We have 46656 - 2*2*2*2*2*2*3*3*3*3*3*3
Grouping the prime factors of 46656 into triples no factor is leftover.