NCERT Solutions for Class 8 Maths Chapter 14 Exercise 14.4 – Factorisation

Download NCERT Solutions for Class 8 Maths Chapter 14 Exercise 14.4 – Factorisation

Find and correct the errors in the following mathematical statements.

1. 4(x – 5) = 4x – 5

Sol.: –

L.H.S. = 4(x – 5)
= 4×x – 4×5
= 4x – 20
≠ R.H.S.
Hence, the correct statement is 4(x – 5) = 4x – 20

2. x(3x + 2) = 3x² + 2

Sol.: –

L.H.S. = x(3x + 2)
= x×3x + x×2
= 3x² +2x
≠ R.H.S.
Hence, the correct statement is x(3x + 2) = 3x² +2x

3. 2x + 3y = 5xy

Sol.: –

L.H.S. = 2x + 3y
= 2x + 3y
≠ R.H.S.
Hence, the correct statement is 2x + 3y = 2x + 3y

4. x + 2x + 3x = 5x

Sol.: –

L.H.S. = x + 2x + 3x
= 1x + 2x + 3x
= 6x
≠ R.H.S.
Hence, the correct statement is x + 2x + 3x = 6x

5. 5y + 2y + y – 7y = 0

Sol.: –

L.H.S. = 5y + 2y + y – 7y
= 5y + 2y + 1y – 7y
= y
≠ R.H.S.
Hence, the correct statement is 5y + 2y + y – 7y = y

6. 3x + 2x = 5x²

Sol.: –

L.H.S. = 3x + 2x
= 5x
≠ R.H.S.
Hence, the correct statement is 3x + 2x = 5x

7. (2x)² + 4(2x) + 7 = 2x² + 8x + 7

Sol.: –

L.H.S. = (2x)² + 4(2x) + 7
= 4x² + 8x +7
≠ R.H.S.
Hence, the correct statement is (2x)² + 4(2x) + 7 = 4x² + 8x +7

8. (2x)² + 5x = 4x + 5x = 9x

Sol.: –

L.H.S. = (2x)² + 5x
= 4x² + 5x
≠ R.H.S.
Hence, the correct statement is (2x)² + 5x = 4x² + 5x

9. (3x + 2)² = 3x² + 6x + 4

Sol.: –

L.H.S. = (3x + 2)²
= (3x)² + 2×3x×2 + 2²   .. { (a + b)² = a² + 2ab + b² }
= 9x² + 12x + 4
≠ R.H.S.
Hence, the correct statement is (3x + 2)² = 9x² + 12x + 4

10. Substituting x = – 3 in

a) x² + 5x + 4 gives (– 3)² + 5 (– 3) + 4 = 9 + 2 + 4 = 15

Sol.: –

L.H.S. = x² + 5x + 4
For x = -3
= (-3)² + 5 × (-3) + 4
= 9 – 15 + 4
= -2
≠ R.H.S.
Hence, the correct statement is x² + 5x + 4 = -2 for x = -3.

b) x² – 5x + 4 gives (– 3)² – 5 (– 3) + 4 = 9 – 15 + 4 = – 2

Sol.: –

L.H.S. = x² – 5x + 4
For x = -3
= (-3)² -5 × (-3) + 4
= 9 + 15 + 4
= 28
≠ R.H.S.
Hence, the correct statement is x² – 5x + 4= 28 for x = -3.

c) x² + 5x gives (– 3)² + 5 (–3) = – 9 – 15 = – 24

Sol.: –

L.H.S. = x² + 5x
For x = -3
= (-3)² + 5 × (-3)
= 9 – 15
= -6
≠ R.H.S.
Hence, the correct statement is x² + 5x = -6 for x = -3.

11. (y – 3)² = y² – 9

Sol.: –

L.H.S. = (y – 3)²
= y² – 2×y×3 + 3²  .. { (a – b)² = a² – 2ab + b² }
= y² – 6y +9
≠ R.H.S.
Hence, the correct statement is (y – 3)² = y² – 6y +9

12. (z + 5)² = z² + 25

Sol.: –

L.H.S. = (z + 5)²
= z² + 2×z×5 + 5²  .. { (a + b)² = a² + 2ab + b² }
= z² + 10z + 25
≠ R.H.S.
Hence, the correct statement is (z + 5)² = z² + 10z + 25

13. (2a + 3b) (a – b) = 2a² – 3b²

Sol.: –

L.H.S. = (2a + 3b) (a – b)
= 2a × a + 2a × (-b) + 3b × a + 3b × (-b)
= 2a² – 2ab + 3ab – 3b²
= 2a² + ab – 3b²
≠ R.H.S.
Hence, the correct statement is (2a + 3b) (a – b) = 2a² + ab – 3b²

14. (a + 4) (a + 2) = a² + 8

Sol.: –

L.H.S. = (a + 4) (a + 2)
= a × a + a × 2 + 4 × a + 4 × 2
= a² + 2a + 4a + 8
= a² + 6a + 8
≠ R.H.S.
Hence, the correct statement is (a + 4) (a + 2) = a² + 6a + 8

15. (a – 4) (a – 2) = a² – 8

Sol.: –

L.H.S. = (a – 4) (a – 2)
= a × a + a × (-2) + (-4) × a + (-4) × (-2)
= a² – 2a – 4a + 8   .. { (x + a)(x + b) = x² + (a + b)x + ab }
= a² – 6a + 8
≠ R.H.S.
Hence, the correct statement is (a – 4) (a – 2) = a² – 6a + 8

16. = 0

Sol.: –

L.H.S. =
= 1
≠ R.H.S.
Hence, the correct statement is = 1

17. = 1+1 = 2

Sol.: –

L.H.S. =
= +
= 1 +
≠ R.H.S.
Hence, the correct statement is = 1 +

18. =

Sol.: –

L.H.S. =
≠ R.H.S.
Hence, the correct statement is =

19. =

Sol.: –

L.H.S. =
≠ R.H.S.
Hence, the correct statement is =

20. = 5

Sol.: –

L.H.S. =
= +
= 1 +
≠ R.H.S.
Hence, the correct statement is

21. = 7x

Sol.: –

L.H.S. =
= +
= + 1
≠ R.H.S.
Hence, the correct statement is = + 1.

Download NCERT Solutions for Class 8 Maths Chapter 14 Exercise 14.4 – Factorisation

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