*According to the CBSE Syllabus 2023-24, this chapter has been renumbered as Chapter 7.
The NCERT Solutions Class 11 Chapter 8 Binomial Theorem can be downloaded at BYJU’S easily. Practising these solutions can help the students clear their doubts as well as solve problems faster. Students can learn new tips and methods to answer a particular question in different ways using NCERT Solutions, which gives them an edge in exam preparation.
The concepts covered in Chapter 8 of the Maths textbook include the study of essential topics such as Positive Integral Indices, Pascal’s Triangle, the Binomial Theorem for any positive integer and some special cases. Students can score high marks in the exams easily by practising the NCERT Class 11 Solutions for all the questions in the textbook. Each solution is solved step-by-step, considering the understanding level of the students. Therefore, it is important to understand the logic set behind each answer and develop a better comprehension of the concepts.
NCERT Solutions for Class 11 Maths Chapter 8 – Binomial Theorem
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Exercise 8.1 Page No: 166
Expand each of the expressions in Exercises 1 to 5.
1. (1 – 2x)5
Solution:
From binomial theorem expansion, we can write as
(1 – 2x)5
= 5Co (1)5 – 5C1 (1)4 (2x) + 5C2 (1)3 (2x)2 – 5C3 (1)2 (2x)3 + 5C4 (1)1 (2x)4 – 5C5 (2x)5
= 1 – 5 (2x) + 10 (4x)2 – 10 (8x3) + 5 ( 16 x4) – (32 x5)
= 1 – 10x + 40x2 – 80x3 + 80x4– 32x5
Solution:
From the binomial theorem, the given equation can be expanded as
3. (2x – 3)6
Solution:
From the binomial theorem, the given equation can be expanded as
Solution:
From the binomial theorem, the given equation can be expanded as
Solution:
From the binomial theorem, the given equation can be expanded as
6. Using the binomial theorem, find (96)3. Â
Solution:
Given (96)3
96 can be expressed as the sum or difference of two numbers, and then the binomial theorem can be applied.
The given question can be written as 96 = 100 – 4
(96)3 = (100 – 4)3
= 3C0 (100)3 – 3C1 (100)2 (4) – 3C2 (100) (4)2– 3C3 (4)3
= (100)3 – 3 (100)2 (4) + 3 (100) (4)2 – (4)3
= 1000000 – 120000 + 4800 – 64
= 884736
7. Using the binomial theorem, find (102)5.
Solution:
Given (102)5
102 can be expressed as the sum or difference of two numbers, and then the binomial theorem can be applied.
The given question can be written as 102 = 100 + 2
(102)5 = (100 + 2)5
= 5C0 (100)5 + 5C1 (100)4 (2) + 5C2 (100)3 (2)2 + 5C3 (100)2 (2)3 + 5C4 (100) (2)4 + 5C5 (2)5
= (100)5 + 5 (100)4 (2) + 10 (100)3 (2)2 + 5 (100) (2)3 + 5 (100) (2)4 + (2)5
= 1000000000 + 1000000000 + 40000000 + 80000 + 8000 + 32
= 11040808032
8. Using the binomial theorem, find (101)4.
Solution:
Given (101)4
101 can be expressed as the sum or difference of two numbers, and then the binomial theorem can be applied.
The given question can be written as 101 = 100 + 1
(101)4 = (100 + 1)4
= 4C0 (100)4 + 4C1 (100)3 (1) + 4C2 (100)2 (1)2 + 4C3 (100) (1)3 + 4C4 (1)4
= (100)4 + 4 (100)3 + 6 (100)2 + 4 (100) + (1)4
= 100000000 + 4000000 + 60000 + 400 + 1
= 104060401
9. Using the binomial theorem, find (99)5m.
Solution:
Given (99)5
99 can be written as the sum or difference of two numbers then the binomial theorem can be applied.
The given question can be written as 99 = 100 -1
(99)5 = (100 – 1)5
= 5C0 (100)5 – 5C1 (100)4 (1) + 5C2 (100)3 (1)2 – 5C3 (100)2 (1)3 + 5C4 (100) (1)4 – 5C5 (1)5
= (100)5 – 5 (100)4 + 10 (100)3 – 10 (100)2 + 5 (100) – 1
= 1000000000 – 5000000000 + 10000000 – 100000 + 500 – 1
= 9509900499
10. Using Binomial Theorem, indicate which number is larger (1.1)10000Â or 1000.
Solution:
By splitting the given 1.1 and then applying the binomial theorem, the first few terms of (1.1)10000 can be obtained as
(1.1)10000 = (1 + 0.1)10000
= (1 + 0.1)10000 C1 (1.1) + other positive terms
= 1 + 10000 × 1.1 + other positive terms
= 1 + 11000 + other positive terms
> 1000
(1.1)10000 > 1000
11. Find (a + b)4 – (a – b)4. Hence, evaluateÂ
Solution:
Using the binomial theorem, the expression (a + b)4 and (a – b)4 can be expanded
(a + b)4 = 4C0 a4 + 4C1 a3 b + 4C2 a2 b2 + 4C3 a b3 + 4C4 b4
(a – b)4 = 4C0 a4 – 4C1 a3 b + 4C2 a2 b2 – 4C3 a b3 + 4C4 b4
Now (a + b)4 – (a – b)4 = 4C0 a4 + 4C1 a3 b + 4C2 a2 b2 + 4C3 a b3 + 4C4 b4 – [4C0 a4 – 4C1 a3 b + 4C2 a2 b2 – 4C3 a b3 + 4C4 b4]
= 2 (4C1 a3 b + 4C3 a b3)
= 2 (4a3 b + 4ab3)
= 8ab (a2 + b2)
Now by substituting a = √3 and b = √2, we get
(√3 + √2)4 – (√3 – √2)4 = 8 (√3) (√2) {(√3)2 + (√2)2}
= 8 (√6) (3 + 2)
= 40 √6
12. Find (x + 1)6 + (x – 1)6. Hence or otherwise evaluateÂ
Â
Solution:
Using binomial theorem, the expressions (x + 1)6 and (x – 1)6 can be expressed as
(x + 1)6 = 6C0 x6 + 6C1 x5 + 6C2 x4 + 6C3 x3 + 6C4 x2 + 6C5 x + 6C6
(x – 1)6 = 6C0 x6 – 6C1 x5 + 6C2 x4 – 6C3 x3 + 6C4 x2 – 6C5 x + 6C6
Now, (x + 1)6 – (x – 1)6 = 6C0 x6 + 6C1 x5 + 6C2 x4 + 6C3 x3 + 6C4 x2 + 6C5 x + 6C6 – [6C0 x6 – 6C1 x5 + 6C2 x4 – 6C3 x3 + 6C4 x2 – 6C5 x + 6C6]
= 2 [6C0 x6 + 6C2 x4 + 6C4 x2 + 6C6]
= 2 [x6 + 15x4 + 15x2 + 1]
Now by substituting x = √2, we get
(√2 + 1)6 – (√2 – 1)6 = 2 [(√2)6 + 15(√2)4 + 15(√2)2 + 1]
= 2 (8 + 15 × 4 + 15 × 2 + 1)
= 2 (8 + 60 + 30 + 1)
= 2 (99)
= 198
13. Show that 9n+1 – 8n – 9 is divisible by 64 whenever n is a positive integer.
Solution:
In order to show that 9n+1 – 8n – 9 is divisible by 64, it has to be shown that 9n+1 – 8n – 9 = 64 k, where k is some natural number.
Using the binomial theorem,
(1 + a)m = mC0 + mC1 a + mC2 a2 + …. + m C m am
For a = 8 and m = n + 1 we get
(1 + 8)n+1 = n+1C0 + n+1C1 (8) + n+1C2 (8)2 + …. + n+1 C n+1 (8)n+1
9n+1 = 1 + (n + 1) 8 + 82 [n+1C2 + n+1C3 (8) + …. + n+1 C n+1 (8)n-1]
9n+1 = 9 + 8n + 64 [n+1C2 + n+1C3 (8) + …. + n+1 C n+1 (8)n-1]
9n+1 – 8n – 9 = 64 k
Where k = [n+1C2 + n+1C3 (8) + …. + n+1 C n+1 (8)n-1] is a natural number
Thus, 9n+1 – 8n – 9 is divisible by 64 whenever n is a positive integer.
Hence proved.
14. Prove thatÂ
Solution:
Exercise 8.2 Page No: 171
Find the coefficient of
1. x5 in (x + 3)8
Solution:
The general term Tr+1 in the binomial expansion is given by Tr+1 = n C r an-r br
Here x5Â is the Tr+1Â term so a= x, b = 3 and n =8
Tr+1 = 8Cr x8-r 3r…………… (i)
To find out x5
We have to equate x5= x8-r
⇒ r= 3
Putting the value of r in (I), we get
= 1512 x5
Hence the coefficient of x5= 1512.
2. a5b7 in (a – 2b)12
Solution:
The general term Tr+1 in the binomial expansion is given by Tr+1 = n C r an-r br
Here a = a, b = -2b & n =12
Substituting the values, we get
Tr+1 = 12Cr a12-r (-2b)r………. (i)
To find a5
We equate a12-r =a5
r = 7
Putting r = 7 in (i)
T8Â =Â 12C7Â a5Â (-2b)7
= -101376 a5Â b7
Hence, the coefficient of a5b7= -101376.
Write the general term in the expansion of
3. (x2 – y)6
Solution:
The general term Tr+1Â in the binomial expansion is given by
Tr+1 = n C r an-r br…….. (i)
Here, a = x2 , n = 6 and b = -y
Putting values in (i)
Tr+1 = 6Cr x 2(6-r) (-1)r yr
= -1r 6cr .x12 – 2r. yr
4. (x2 – y x)12, x ≠0
Solution:
The general term Tr+1 in the binomial expansion is given by Tr+1 = n C r an-r br
Here n = 12, a= x2Â and b = -y x
Substituting the values, we get
Tn+1 =12Cr × x2(12-r) (-1)r yr xr
= -1r 12cr .x24 –2r. yr
5. Find the 4th term in the expansion of (x – 2y)12.
Solution:
The general term Tr+1 in the binomial expansion is given by Tr+1 = n C r an-r br
Here, a= x, n =12, r= 3 and b = -2y
By substituting the values, we get
T4Â =Â 12C3Â x9Â (-2y)3
= -1760 x9Â y3
6. Find the 13th term in the expansion ofÂ
Solution:
Find the middle terms in the expansions of
Solution:
Solution:
9. In the expansion of (1 + a)m+n, prove that coefficients of am and an are equal.
Solution:
We know that the general term Tr+1 in the binomial expansion is given by Tr+1 = nCr an-r br
Here n= m+n, a = 1 and b= a
Substituting the values in the general form
Tr+1 = m+n Cr 1m+n-r ar
= m+n Cr ar…………. (i)
Now, we have that the general term for the expression is,
Tr+1 =  m+n Cr ar
Now, for coefficient of am
Tm+1 =  m+n Cm am
Hence, for the coefficient of am, the value of r = m
So, the coefficient is m+n C m
Similarly, the coefficient of an is m+n C n
10. The coefficients of the (r – 1)th, rth and (r + 1)th terms in the expansion of (x + 1)n are in the ratio 1:3:5. Find n and r.
Solution:
The general term Tr+1 in the binomial expansion is given by Tr+1 = nCr an-r br
Here, the binomial is (1+x)n with a = 1 , b = x and n = n
The (r+1)th term is given by
T(r+1) = nCr 1n-r xr
T(r+1) = nCr xr
The coefficient of (r+1)th term is nCr
The rth term is given by (r-1)th term
T(r+1-1)Â =Â nCr-1Â xr-1
Tr = nCr-1 xr-1
∴ the coefficient of rth term is nCr-1
For (r-1)th term, we will take (r-2)th term
Tr-2+1Â =Â nCr-2Â xr-2
Tr-1Â =Â nCr-2Â xr-2
∴ the coefficient of (r-1)th term is nCr-2
Given that the coefficient of (r-1)th, rth and r+1th term are in ratio 1:3:5
Therefore,
⇒ 5r = 3n – 3r + 3
⇒ 8r – 3n – 3 =0………….2
We have 1 and 2 as
n – 4r ± 5 =0…………1
8r – 3n – 3 =0…………….2
Multiplying equation 1 by number 2
2n -8r +10 =0……………….3
Adding equations 2 and 3
2n -8r +10 =0
-3n – 8r – 3 =0
⇒ -n = -7
n =7Â and r = 3
11. Prove that the coefficient of xn in the expansion of (1 + x)2n is twice the coefficient of xn in the expansion of (1 + x)2n – 1.
Solution:
The general term Tr+1 in the binomial expansion is given by Tr+1 = nCr an-r br
The general term for binomial (1+x)2n is
Tr+1 = 2nCr xr …………………..1
To find the coefficient of xn
r = n
Tn+1 = 2nCn xn
The coefficient of xn = 2nCn
The general term for binomial (1+x)2n-1Â is
Tr+1 = 2n-1Cr xr
To find the coefficient of xn
Putting n = r
Tr+1 = 2n-1Cr xn
The coefficient of xn = 2n-1Cn
We have to prove
Coefficient of xn in (1+x)2n = 2 coefficient of xn in (1+x)2n-1
Consider LHS = 2nCn
12. Find a positive value of m for which the coefficient of x2 in the expansion (1 + x)m is 6.
Solution:
The general term Tr+1 in the binomial expansion is given by Tr+1 = nCr an-r br
Here, a = 1, b = x and n = m
Putting the value
Tr+1 = m Cr 1m-r xr
= m Cr xr
We need the coefficient of x2
∴ putting r = 2
T2+1Â =Â mC2Â x2
The coefficient of x2Â =Â mC2
Given that coefficient of x2 = mC2 = 6
⇒ m (m – 1) = 12
⇒ m2– m – 12 =0
⇒ m2– 4m + 3m – 12 =0
⇒ m (m – 4) + 3 (m – 4) = 0
⇒ (m+3) (m – 4) = 0
⇒ m = – 3, 4
We need the positive value of m, so m = 4
Miscellaneous Exercise Page No: 175
1. Find a, b and n in the expansion of (a + b)n if the first three terms of the expansion are 729, 7290 and 30375, respectively.
Solution:
We know that (r + 1)th term, (Tr+1), in the binomial expansion of (a + b)n is given by
Tr+1 = nCr an-t br
The first three terms of the expansion are given as 729, 7290 and 30375, respectively. Then we have,
T1 = nC0 an-0 b0 = an = 729….. 1
T2 = nC1 an-1 b1 = nan-1 b = 7290…. 2
T3 = nC2 an-2 b2 = {n (n -1)/2 }an-2 b2 = 30375……3
Dividing 2 by 1, we get
Dividing 3 by 2, we get
From 4 and 5, we have
n. 5/3 = 10
n = 6
Substituting n = 6 in 1, we get
a6 = 729
a = 3
From 5, we have, b/3 = 5/3
b = 5
Thus a = 3, b = 5 and n = 76
2. Find a if the coefficients of x2Â and x3Â in the expansion of (3 + a x)9Â are equal.
Solution:
3. Find the coefficient of x5 in the product (1 + 2x)6 (1 – x)7 using binomial theorem.
Solution:
(1 + 2x)6 = 6C0 + 6C1 (2x) + 6C2 (2x)2 + 6C3 (2x)3 + 6C4 (2x)4 + 6C5 (2x)5 + 6C6 (2x)6
= 1 + 6 (2x) + 15 (2x)2 + 20 (2x)3 + 15 (2x)4 + 6 (2x)5 + (2x)6
= 1 + 12 x + 60x2 + 160 x3 + 240 x4 + 192 x5 + 64x6
(1 – x)7 = 7C0 – 7C1 (x) + 7C2 (x)2 – 7C3 (x)3 + 7C4 (x)4 – 7C5 (x)5 + 7C6 (x)6 – 7C7 (x)7
= 1 – 7x + 21x2 – 35x3 + 35x4 – 21x5 + 7x6 – x7
(1 + 2x)6 (1 – x)7 = (1 + 12 x + 60x2 + 160 x3 + 240 x4 + 192 x5 + 64x6) (1 – 7x + 21x2 – 35x3 + 35x4 – 21x5 + 7x6 – x7)
192 – 21 = 171
Thus, the coefficient of x5Â in the expression (1+2x)6(1-x)7 is 171.
4. If a and b are distinct integers, prove that a – b is a factor of an – bn, whenever n is a positive integer. [Hint write an = (a – b + b)n and expand]
Solution:
In order to prove that (a – b) is a factor of (an – bn), it has to be proved that
an – bn = k (a – b) where k is some natural number.
a can be written as a = a – b + b
an = (a – b + b)n = [(a – b) + b]n
= nC0 (a – b)n + nC1 (a – b)n-1 b + …… + n C n bn
an – bn = (a – b) [(a –b)n-1 + nC1 (a – b)n-1 b + …… + n C n bn]
an – bn = (a – b) k
Where k = [(a –b)n-1 + nC1 (a – b)n-1 b + …… + n C n bn] is a natural number
This shows that (a – b) is a factor of (an – bn), where n is a positive integer.
5. EvaluateÂ
Solution:
Using the binomial theorem, the expression (a + b)6 and (a – b)6 can be expanded
(a + b)6 = 6C0 a6 + 6C1 a5 b + 6C2 a4 b2 + 6C3 a3 b3 + 6C4 a2 b4 + 6C5 a b5 + 6C6 b6
(a – b)6 = 6C0 a6 – 6C1 a5 b + 6C2 a4 b2 – 6C3 a3 b3 + 6C4 a2 b4 – 6C5 a b5 + 6C6 b6
Now (a + b)6 – (a – b)6 =6C0 a6 + 6C1 a5 b + 6C2 a4 b2 + 6C3 a3 b3 + 6C4 a2 b4 + 6C5 a b5 + 6C6 b6 – [6C0 a6 – 6C1 a5 b + 6C2 a4 b2 – 6C3 a3 b3 + 6C4 a2 b4 – 6C5 a b5 + 6C6 b6]
Now by substituting a = √3 and b = √2, we get
(√3 + √2)6 – (√3 – √2)6 = 2 [6 (√3)5 (√2) + 20 (√3)3 (√2)3 + 6 (√3) (√2)5]
= 2 [54(√6) + 120 (√6) + 24 √6]
= 2 (√6) (198)
= 396 √6
6. Find the value ofÂ
Solution:
7. Find an approximation of (0.99)5Â using the first three terms of its expansion.
Solution:
0.99 can be written as
0.99 = 1 – 0.01
Now by applying the binomial theorem, we get
(o. 99)5 = (1 – 0.01)5
= 5C0 (1)5 – 5C1 (1)4 (0.01) + 5C2 (1)3 (0.01)2
= 1 – 5 (0.01) + 10 (0.01)2
= 1 – 0.05 + 0.001
= 0.951
8. Find n, if the ratio of the fifth term from the beginning to the fifth term from the end, in the expansion of , is √6: 1
Solution:
9. Expand using the Binomial TheoremÂ
Solution:
Using the binomial theorem, the given expression can be expanded as
Again by using the binomial theorem to expand the above terms, we get
From equations 1, 2 and 3, we get
10. Find the expansion of (3x2 – 2ax + 3a2)3 using binomial theorem.
Solution:
We know that (a + b)3Â = a3Â + 3a2b + 3ab2Â + b3
Putting a = 3x2Â & b = -a (2x-3a), we get
[3x2Â + (-a (2x-3a))]3= (3x2)3+3(3x2)2(-a (2x-3a)) + 3(3x2) (-a (2x-3a))2Â + (-a (2x-3a))3
= 27x6Â – 27ax4 (2x-3a) + 9a2x2 (2x-3a)2Â – a3(2x-3a)3
=Â 27x6Â – 54ax5Â + 81a2x4Â +Â 9a2x2 (4x2-12ax+9a2) – a3 [(2x)3Â – (3a)3Â – 3(2x)2(3a) + 3(2x)(3a)2]
=Â 27x6Â – 54ax5Â + 81a2x4Â +Â 36a2x4Â – 108a3x3Â + 81a4x2 – 8a3x3Â + 27a6Â + 36a4x2Â – 54a5x
=Â 27x6Â – 54ax5+Â 117a2x4Â – 116a3x3Â + 117a4x2Â – 54a5x + 27a6
Thus, (3x2 – 2ax + 3a2)3
=Â 27x6Â – 54ax5+Â 117a2x4Â – 116a3x3Â + 117a4x2Â – 54a5x + 27a6
Also Access |
NCERT Exemplar for Class 11 Maths Chapter 8 |
CBSE Notes for Class 11 Maths Chapter 8 |
NCERT Solutions for Class 11 Maths Chapter 8 – Binomial Theorem
The Chapter 8 Binomial Theorem of NCERT Solutions for Class 11 covers the topics given below.
8.1 Introduction to Binomial TheoremÂ
8.2 Binomial Theorem for Positive Integral IndicesÂ
    Pascal’s TriangleÂ
8.2.1 Binomial theorem for any positive integer nÂ
8.2.2 Some special cases
8.3 General and Middle TermsÂ
Exercise 8.1 Solutions 14 Questions
Exercise 8.2 Solutions 12 Questions
Miscellaneous Exercise On Chapter 8 Solutions 10 Questions
NCERT Solutions for Class 11 Maths Chapter 8 – Binomial Theorem
The unit Algebra houses the chapter Binomial Theorem, adding up to 30 marks of the total 80 marks. A total of 3 exercises, including the miscellaneous exercise, are present in this chapter. Chapter 8 of NCERT Solutions for Class 11 Maths discusses the concepts provided underneath:
- The expansion of a binomial for any positive integral n is given by the Binomial Theorem, which is (a+b)n = nC0 an + nC1 an – 1b + nC2 an – 2b2 + …+ nCn – 1a.bn – 1 + nCn bn .
- The coefficients of the expansions are arranged in an array. This array is called Pascal’s triangle.
- The general term of an expansion (a + b)n is Tr + 1 = nCr an – r. br
Therefore, it is ensured that a student who is thorough with Chapter 8 of Class 11, the Binomial Theorem, will be well-versed in the history of the Binomial Theorem, statement and proof of the binomial theorem for positive integral indices, Pascal’s triangle, general and middle term in binomial expansion as well as simple applications of Binomial theorem.
Disclaimer –Â
Dropped Topics –Â
8.3 General Middle Terms
Example 17 and Ques. 1–3, and 8 (Miscellaneous Exercise)
Last two points in the Summary
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