Ncert Solutions For Class 8 Maths Ex 14.4

Ncert Solutions For Class 8 Maths Chapter 14 Ex 14.4

 Question 1:

Find the error in the following statement and correct it: 5(a – 4) = 5a – 4

sol.

L.H.S. = 5(a – 4) = 5a – 20 ≠ R.H.S.

Hence, the correct statement is 5a – 20.

Question 2:

Find the error in the following statement and correct it: a(3a + 2) = 3a2 + 2

sol.

L.H.S. = a(3a + 2) = 3a2 + 2a ≠ R.H.S.

Hence, the correct statement is a(3a + 2) = 3a2 + 2a.

Question 3:

Find the error in the following statement and correct it: 2a + 3b = 5ab

sol.

L.H.S. = 2a + 3b ≠ R.H.S.

Hence, the correct statement is 2a + 3b = 2a + 3b.

 

Question 4:

Find the error in the following statement and correct it: a + 2a + 3a = 5a

sol.

L.H.S. = a + 2a + 3a = 6a ≠ R.H.S.

Hence, the correct statement is a + 2a + 3a = 6a.

 

Question 5:

Find the error in the following statement and correct it: 5b + 2b + b – 7b = 0

sol.

L.H.S. = 5b + 2b + b – 7b = b ≠ R.H.S.

Hence, the correct statement is 5b + 2b + b – 7b = b.

 

Question 6:

Find the error in the following statement and correct it: 3a + 2a = 5a2

sol.

L.H.S. = 3a + 2a = 5a ≠ R.H.S.

Hence, the correct statement is 3a + 2a = 5a.

 

Question 7:

Find the error in the following statement and correct it: (2a)2 + 4(2a) + 7 = 2a2 + 8a + 7

sol.

L.H.S. = (2a)2 + 4(2a) + 7 = 4a2 + 8a + 7 ≠ R.H.S.

Hence, the correct statement is (2a)2 + 4(2a) + 7 = 4a2 + 8a + 7.

 

Question 8:

Find the error in the following statement and correct it: (2a)2 + 5a = 4a + 5a = 9a

sol.

L.H.S. = (2a)2 + 5a = 4a2 + 5a ≠ R.H.S.

Hence, the correct statement is (2a)2 + 5a = 4a2 + 5a.

 

Question 9:

Find the error in the following statement and correct it: (3a + 2)2 = 3a2 + 6a + 4

sol.

L.H.S. = (3a + 2)2 = (3a)2 + 2 x 3a x 2 + (2)2 = 9a2 + 12a + 4 ≠ R.H.S.

Hence, the correct statement is (3a + 2)2 = 9a2 + 12a + 4.

 

Question 10:

Find the error in the following statement and correct it:

Substituting a = -3 in:

i) a2 + 5a + 4 gives 15

ii) a2 – 5a + 4 gives -2

iii) a2 + 5a = -24

sol.

i) L.H.S. = a2 + 5a + 4

Substituting a= -3,

= (-3)2 + 5(-3) + 4

= 9 – 15 + 4

= -2 ≠ R.H.S.

Hence, a2 + 5a + 4 = -2.

 

ii) L.H.S. = a2 – 5a + 4

Substituting a= -3,

= (-3)2 – 5(-3) + 4

= 9 + 15 + 4

= 28 ≠ R.H.S.

Hence, a2 – 5a + 4 = 28.

 

iii) L.H.S. =  a2 + 5a

Substituting a= -3,

= (-3)2 + 5(-3)

= 9 – 15

=-6 ≠ R.H.S.

Hence,  a2 + 5a = -6.

 

Question 11:

Find the error in the following statement and correct it: (b – 3)2 = b2 – 9.

sol.

L.H.S. = (b – 3)2 = b2 – 2 x b x 3 + (3)2 = b2 – 6b + 9 ≠ R.H.S.

Hence, the correct statement is (b – 3)2 = b2 – 6b + 9.

 

 

Question 12:

Find the error in the following statement and correct it: (c + 5)2 = c2 +25.

sol.

L.H.S. = (c + 5)2 = c2 + 2 x c x 5 + (5)2 = c2 – 10b + 25 ≠ R.H.S.

Hence, the correct statement is (c + 5)2 = c2 – 10b + 25.

 

Question 13:

Find the error in the following statement and correct it: (2x + 3y)(x – y) = 2x2 – 3y2.

sol.

L.H.S. = (2x + 3y)(x – y) = 2x(x – y) + 3y(x – y)

= 2x2 – 2ab + 3ab – 3b2 = 2a2 + ab – 3b2 ≠ R.H.S.

Hence, the correct statement is (2x + 3y)(x – y) = 2a2 + ab – 3b2.

 

Question 14:

Find the error in the following statement and correct it: (x + 4)(x + 2) = x2 + 8.

sol.

L.H.S. = (x + 4)(x + 2) = x(x +2) + 4(x + 2)

= x2 + 2x + 4x + 8 = x2 + 6x + 8 ≠ R.H.S.

Hence, the correct statement is (x + 4)(x + 2) = 2a2 + x2 + 6x + 8.

 

Question 15:

Find the error in the following statement and correct it: 3x23x2=0

sol.

L.H.S. = 3x23x2=11=1 ≠ R.H.S.

Hence, the correct statement is 3x23x2=1.

 

 

Question 16:

Find the error in the following statement and correct it: 3x2+13x2=1+1=2

sol.

L.H.S. = 3x2+13x2=3x23x2+13x2=1+13x2 ≠ R.H.S.

Hence, the correct statement is 3x2+13x2=1+13x2.

 

Question 17:

Find the error in the following statement and correct it: 3x3x+2=12

sol.

L.H.S. = 3x3x+2 ≠ R.H.S.

Hence, the correct statement is 3x3x+2=3x3x+2.

 

Question 18:

Find the error in the following statement and correct it: 34x+3=14x

sol.

L.H.S. = 34x+3 ≠ R.H.S.

Hence, the correct statement is 34x+3=34x+3.

 

Question 19:

Find the error in the following statement and correct it: 4x+54x=5

sol.

L.H.S. = 4x+54x=4x4x+54x=1+54x ≠ R.H.S.

Hence, the correct statement is 4x+54x=1+54x.

 

Question 20:

Find the error in the following statement and correct it: 7x+55=7x

sol.

L.H.S. = 7x+55=7x5+55=7x5+1 ≠ R.H.S.

Hence, the correct statement is 7x+55=7x5+1.