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MATHEMATICS

EXERCISE 7.1

1. Which of the following numbers are not perfect cubes?
1. 216
2. 46656
3. 128
4. 1000
5. 100


Sagot :

To determine if a number is a perfect cube, we need to check if there exists an integer [tex]\( n \)[/tex] such that [tex]\( n^3 \)[/tex] equals the given number. Below is the step-by-step process for each number provided in the question.

1. 216
We check if there is an integer [tex]\( n \)[/tex] such that [tex]\( n^3 = 216 \)[/tex].
- [tex]\( 6^3 = 216 \)[/tex].
Hence, 216 is a perfect cube.

2. 46656
We check if there is an integer [tex]\( n \)[/tex] such that [tex]\( n^3 = 46656 \)[/tex].
- [tex]\( 36^3 = 46656 \)[/tex].
Hence, 46656 is a perfect cube.

3. 128
We check if there is an integer [tex]\( n \)[/tex] such that [tex]\( n^3 = 128 \)[/tex].
- [tex]\( 5^3 = 125 \)[/tex] and [tex]\( 6^3 = 216 \)[/tex]; 128 does not fall between these cubes perfectly.
Hence, 128 is not a perfect cube.

4. 1000
We check if there is an integer [tex]\( n \)[/tex] such that [tex]\( n^3 = 1000 \)[/tex].
- [tex]\( 10^3 = 1000 \)[/tex].
Hence, 1000 is a perfect cube.

5. 100
We check if there is an integer [tex]\( n \)[/tex] such that [tex]\( n^3 = 100 \)[/tex].
- [tex]\( 4^3 = 64 \)[/tex] and [tex]\( 5^3 = 125 \)[/tex]; 100 does not fall between these cubes perfectly.
Hence, 100 is not a perfect cube.

Therefore, the numbers that are not perfect cubes are:
(ii) 128 and (iv) 100.
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