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Binomial Theorem

JEE Main 2024 (Online) 8th April Morning ShiftNumericalMedium📈 Topic in 43% papers+4
Ques. 1JEE Main 2024, 8 April (Morning Shift)

Let = r=0n (4r2 + 2r + 1 )nCr and = ( r=0n nCrr + 1 ) + 1n + 1. If 140 < 2 < 281, then the value of n is .

Answer

5

Solution

Use nCr = 2n, r nCr = n 2n-1, r2 nCr = n(n + 1)2n-2

= 4n(n + 1)2n-2 + 2n 2n-1 + 2n = 2n [n(n + 1) + n + 1 ] = 2n(n + 1)2

nCrr + 1 = n+1Cr+1n + 1 r=0n nCrr + 1 = 2n+1 - 1n + 1

= 2n+1 - 1 + 1n + 1 = 2n+1n + 1

2 = 2n+1(n + 1)2 (n + 1)2n+1 = (n + 1)3

140 < (n + 1)3 < 281, and the only cube in this range is 216 = 63 (53 = 125, 73 = 343)

So n + 1 = 6, i.e. n = 5

Answer: 5

Keep practising — Binomial Theorem

Ques. 2JEE Main 2024, 8 April (Evening Shift)

If the term independent of x in the expansion of ( ax2 + 12x3 )10 is 105, then a2 is equal to :

  1. 6
  2. 4
  3. 2
  4. 9
Ques. 3JEE Main 2024, 6 April (Morning Shift)

If the second, third and fourth terms in the expansion of (x + y)n are 135, 30 and 103, respectively, then 6 (n3 + x2 + y ) is equal to .

Ques. 4JEE Main 2024, 5 April (Morning Shift)

If the constant term in the expansion of (1 + 2x - 3x3 ) ( 32x2 - 13x )9 is p, then 108p is equal to .

Ques. 5JEE Main 2024, 5 April (Evening Shift)

If the constant term in the expansion of ( [5]3x + 2x [3]5 )12, x 0, is 28 [5]3, then 25 is equal to :

  1. 724
  2. 742
  3. 693
  4. 639
Ques. 6JEE Main 2024, 4 April (Morning Shift)

The sum of all rational terms in the expansion of (2 15+5 13 )15 is equal to :

  1. 633
  2. 6131
  3. 3133
  4. 931
Ques. 7JEE Main 2024, 4 April (Evening Shift)

If the coefficients of x4, x5 and x6 in the expansion of (1 + x)n are in the arithmetic progression, then the maximum value of n is:

  1. 28
  2. 21
  3. 7
  4. 14
Ques. 8JEE Main 2024, 1 February (Morning Shift)

If the coefficient of x30 in the expansion of (1+ 1x )6 (1+x2 )7 (1-x3 )8; x 0 is , then | | equals .

Ques. 9JEE Main 2024, 1 February (Evening Shift)

Let m and n be the coefficients of seventh and thirteenth terms respectively in the expansion of ( 13x 13+ 12x 23 )18. Then ( nm ) 13 is :

  1. 19
  2. 14
  3. 49
  4. 94
Ques. 10JEE Main 2024, 31 January (Morning Shift)

In the expansion of (1+x) (1-x2 ) (1+ 3x+ 3x2+ 1x3 )5, x 0, the sum of the coefficients of x3 and x-13 is equal to .

Ques. 11JEE Main 2024, 31 January (Evening Shift)

Let the coefficient of xr in the expansion of (x+3)n-1+(x+3)n-2(x+2)+(x+3)n-3(x+2)2+ +(x+2)n-1 be r. If r=0n r= n- n, , N, then the value of 2+ 2 equals .

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