All questions of Binomial Theorem for Mathematics Exam

The number of terms in the expansion of (2x + 3y- 4z)n is 
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'C'. Can you explain this answer?

Veda Institute answered
We have, (2x + 3y - 4z)n = {2 + (3 - 4)}n


Clearly, the first term in the above   expansion gives one term, second term gives two terms, third term gives three terms and so on.
So, Total  number of term = 1 +2+3+...+n+(n+1) = 

The number of irrational terms in the expansion of  (21/5 +31/10)55 is 
  • a)
    47
  • b)
    56
  • c)
    50
  • d)
    48 
Correct answer is option 'C'. Can you explain this answer?

Chirag Verma answered
(21/531/10)55 
Total terms = 55 + 1 = 56 

Here r = 0, 10, 20, 30, 40, 50
Number of rational terms = 6;  
Number of irrational terms = 56 - 6 = 50

The sum rCr + r+1Cr + r+2Cr + .... + nCr (n > r) equals  
  • a)
    nCr+1
  • b)
    n+1Cr+1
  • c)
    n+1Cr-1
  • d)
    n+1Cr
Correct answer is option 'B'. Can you explain this answer?

Chirag Verma answered
C(n, r) + c(n ‐1, r) + C(n ‐ 2, r) + . . . + C(r, r)

= n+1Cr+1 (applying same rule again and again)
(∵ nCr + nCr‐1 = n+1Cr)

If in the expansion of (1 + x)m(1 - x)n, the coefficient of x and x2 are 3 and -6 respectively, then m is 
  • a)
    6
  • b)
    9
  • c)
    12
  • d)
    24 
Correct answer is option 'C'. Can you explain this answer?

Chirag Verma answered



⇒ m2 - m2 + n - n - 2mn = -12
⇒ (m - n)2 - (m + n) = -12 ⇒ m + n = 9 + 12 = 21      (2) using (1)
Solving (1) and (2), we get m = 12.

The number of irrational terms in the expansion of (21/5 + 31/10)55 is
  • a)
    47  
  • b)
    56  
  • c)
    50  
  • d)
    48  
Correct answer is option 'C'. Can you explain this answer?

Chirag Verma answered
(21/5 + 31/10)55
Total terms = 55 + 1 = 56

Here r = 0, 10, 20, 30, 40, 50
Number of rational terms = 6;
Number of irrational terms = 56 ‐ 6 = 50

The term independent of x in 
  • a)
    5
  • b)
    7
  • c)
    6
  • d)
Correct answer is option 'C'. Can you explain this answer?

Chirag Verma answered
The general term 
The term  independent  of x, (or  the constant term) corresponds to x18-3r being  x0 or 18 - 3r = 0 ⇒ r = 6 .

Coefficient of x4 in (1 + x – 2x2)6 is
  • a)
    –60
  • b)
    –45
  • c)
    45
  • d)
    15
Correct answer is option 'B'. Can you explain this answer?

Ayush Mehra answered


Expanding the expression

To find the coefficient of \(x^4\) in the given expression \((1 + x – 2x^2)^6\), we need to expand the expression using the binomial theorem.

Binomial theorem

The binomial theorem states that for any real numbers a and b, and any non-negative integer n, the expansion of \((a + b)^n\) can be written as the sum of terms of the form \({n \choose k} a^{n-k} b^k\), where \({n \choose k}\) is the binomial coefficient.

Coefficient of x^4

To find the coefficient of \(x^4\) in the expansion, we need to look for terms of the form \(x^4\) in the expanded expression. This can be achieved by finding all possible combinations of terms from the base expression \((1 + x – 2x^2)\) that multiply to give \(x^4\).

Calculating the coefficient

When expanding the given expression, the term that contributes to \(x^4\) is \({6 \choose 2} \cdot 1^4 \cdot x^4 \cdot (-2x^2)^2\). Calculating this term gives \({6 \choose 2} \cdot 1^4 \cdot x^4 \cdot 4x^4 = 15 \cdot 1 \cdot 4 = 60\).

Therefore, the coefficient of \(x^4\) in the expression \((1 + x – 2x^2)^6\) is 60.

So, option B (-45) is not correct.

The number of irrational terms in the expansion of (21/5 + 31/10)55 is
  • a)
    47
  • b)
    56
  • c)
    50
  • d)
    48 
Correct answer is option 'C'. Can you explain this answer?

Chirag Verma answered
(21/5 + 31/10)55 Total terms = 55 + 1 = 56 

Here  r = 0, 10, 20, 30, 40, 50
Number of  rational terms = 6;  
Number of irrational terms = 56 - 6 = 50

The sum rCr + r+1Cr + r+2Cr + .....+ nCr (n > r) equals
  • a)
    nCr +1
  • b)
    n +1Cr+1
  • c)
    n +1Cr-1
  • d)
    n +1Cr
Correct answer is option 'B'. Can you explain this answer?

Chirag Verma answered
C(n, r)  + c(n -1, r)  +  C(n - 2, r) +  ...  + C(r, r)
= r+1Cr+1 + r+1Cr + r+2Cr + .... +  n-1Cr + nCr
= n+1Cr+1   (applying same rule again and again )        (∴ nCr + nCr-1 = n+1Cr)

If 22006 - 2006 divided by 7, the remainder is
  • a)
    0
  • b)
    1
  • c)
    2
  • d)
    4
Correct answer is option 'A'. Can you explain this answer?

Gaurav Rao answered
Problem:
Find the remainder when 22006 - 2006 is divided by 7.

Solution:
To find the remainder when a number is divided by another number, we can use the concept of congruence. Two numbers are said to be congruent modulo n if their difference is divisible by n.

Let's represent the given expression as a congruence equation:
22006 - 2006 ≡ x (mod 7)

Step 1: Simplify the expression on the left side of the congruence equation.
22006 - 2006 = 20000

The congruence equation becomes:
20000 ≡ x (mod 7)

Step 2: Find the remainder when 20000 is divided by 7.
To find the remainder, we divide 20000 by 7 and observe the remainder.

20000 ÷ 7 = 2857 remainder 1

Therefore, 20000 leaves a remainder of 1 when divided by 7.

Step 3: Substitute the remainder in the congruence equation.
x ≡ 1 (mod 7)

Answer:
The remainder when 22006 - 2006 is divided by 7 is 1. Therefore, option 'A' is the correct answer.

The numbers of  terms in the expansion of 
  • a)
    201
  • b)
    300
  • c)
    200
  • d)
    100C3
Correct answer is option 'A'. Can you explain this answer?

Chirag Verma answered


Where ao = sum of all absolute terms   = 1 +100 C2 .2 + ....
Similarly  a1, a2 , ...a100 and  b1, b2 ...b100 are coefficients obtained after simplification.
∴ Total number of terms = 1 + 100 + 100 = 201

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