CLASS VIII MATHS CUBE AND CUBE ROOTS

Cube and cube roots

1. Cube Roots

2. To understand cube roots, first, we must understand cubes…… HOW TO CUBE A NUMBER: To cube a number, just multiply a number by itself 3 times. For e.g. 3 cubed = 3 3 = 3 x 3 x 3 = 27 3 3 3

3. Some more examples of cubes: 4 = 64 5 3 = 125 7 3 = 343 2 3 = 8 1 3 = 1 3 3 = 27 6 3 = 216 8 3 = 512 9 3 = 729 10 3 = 1000

4.   3 CUBE ROOTS

5. CUBE ROOTS   Taking the Cube root of a perfect cube will give you the dimension of one edge of the cube 3 3   = 3 3 3 27

6. The Cube Root Symbol!! This is the special symbol that means ‘cube root’. It is the RADICAL symbol (used for square roots also), with a little three to mean cube root. This would be said, the cube root of 27 equals 3.

7. CUBE ROOT: Just like square roots are the opposite of squaring a number, cube roots, are the opposite of cubing a number. A cube root goes in the other direction: INVERSE OPERATIONS   4 3 3 x x 3

8. These are some of the PERFECT CUBES of whole numbers!

9. Finding cube roots using prime factorisation 8000 = 2x2x2 x 2x2x2 x 5x5x5 So, 8000 = 2 x 2 x 5 3

10. Finding cube roots using estimation Step 1- Form groups of three starting from the right most digit. Example 17 576

11. Finding cube roots using estimation Step 2- Take 576 The digit is 6 at one’s place. We will now take 6 as required cube’s one place. Required cube = _ 6

12. Finding cube roots using estimation Step 3- Then take the other group that is 17. Cube of 2=8 and cube of 3=27. So, 17 lies between 2 and 3 and the smallest number between them is 2. Take 2 as required cube’s tens place Required cube = 2 6 = Answer

13. THANKS