West Bengal - Mathematics

5. Cubes

1. Revision
2. Pie Chart
3. Rational Numbers
4. Multiplication and Division of Polynomials
5. Cubes
6. Complementary Angles, Suplementary Angles and Adjacent Angles
7. Concept of Vertically Opposite Angles
8. Properties of Parallel Lines and Their Transversal
9. Relation Between the Two Sides of a Triangle and Their Opposite Angles
10. Rule of Three
11. Percentage
12. Mixture
13. Factorisation of Algebraic Expressions
14. HCF and LCM of Algebraic Expression
15. Simplification of Algebraic Expression
16. Verification of the Relation Between the Angles and Sides of a Triangle
17. Time and Work
18. Graphs
19. Formation of an Equation and its Solution
20. Geometrical Proofs
21. Construction of Triangles
22. Construction of Parallel Lines
23. Dividing a Line Segment into Three or Five Equal Parts

Lets Do 5.1

Lets Work Out 5.1

Lets Work Out 5.2

Lets Work Out 5.3

Q. 3

Let’s find the value of by calculation if

or,

or,

or, [by transposition]

[With the help of the identity No. VI]

Class 8th West Bengal - Mathematics 5. Cubes

Answer :

Given,

Multiplying both side by ‘x’

⇒ x² + 1 = -x

⇒ x² + x + 1 = 0

Now,

x³ – 1

Using x³ – y³ = (x – y)(x² + xy + y²)

= (x – 1)(x² + x + 1)

= (x – 1) × 0

= 0

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[With the help of the identity No. VI]

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West Bengal - Mathematics