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Suppose 2 - p, p, 2 - alpha, alpha are the coefficient of four consecutive terms in the expansion of (1 + x)^n . Then the value of p^2 - alpha^2 + 6alpha + 2p equals

Solution & Explanation

### Related Formula textCoefficient of (r+1)^textth text term in (1+x)^n text is ^nC_r ^nC_r + ^nC_r+1 = ^n+1C_r+1 ### Core Logic Let the four consecutive binomial coefficients be ^nC_r, ^nC_r+1, ^nC_r+2, ^nC_r+3. Given these correspond to 2 - p, p, 2 - alpha, alpha respectively. From the properties of combinations: ^nC_r + ^nC_r+1 = (2 - p) + p = 2 Rightarrow ^n+1C_r+1 = 2 quad dots(1) Similarly: ^nC_r+2 + ^nC_r+3 = (2 - alpha) + alpha = 2 Rightarrow ^n+1C_r+3 = 2 quad dots(2) ### Step 1: Identifying the Inconsistency From equations (1) and (2): ^n+1C_r+1 = ^n+1C_r+3 = 2 By combination properties, if ^nC_x = ^nC_y and x neq y, then x + y = n. So, (r+1) + (r+3) = n+1 Rightarrow 2r + 4 = n+1 Rightarrow n = 2r + 3. Substitute n back into the equality: ^2r+4C_r+1 = 2 The binomial coefficient must be ge 2. However, for any valid integer r ge 0, ^2r+4C_r+1 grows very rapidly. Let's test small values: If r = 0, ^4C_1 = 4 neq 2. If r = 1, ^6C_2 = 15 neq 2. Hence, no integer values satisfy this condition, making the given data inherently inconsistent. ### Step 2: Conclusion Due to inconsistent data resulting in a mathematically impossible scenario, this question was treated as a Bonus/Dropped question. ### Pattern Recognition Adding consecutive binomial coefficients yields the sum from Pascal's triangle identity ^nC_r + ^nC_r+1 = ^n+1C_r+1. If identical sums yield small integer invariants like 2, they typically break bounding limits for ^nC_k combinations. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Maths: Binomial Theorem

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More Binomial Theorem Previous-Year Questions — Page 4

Q68 jee_main_2025_28_jan_evening Properties of Coefficients and Rational Terms
Let the coefficients of three consecutive terms T_r, T_r+1 and T_r+2 in the binomial expansion of (a+b)^12 be in a G.P. and let p be the number of all possible values of r. Let q be the sum of all rational terms in the binomial expansion of (sqrt[4]3+sqrt[3]4)^12 . Then p+q is equal to :
  • A. 283
  • B. 295
  • C. 287
  • D. 299

Solution

### Related Formula General term of binomial expansion (x + y)^n: T_k+1 = binomnk x^n-k y^k Condition for three terms A, B, C to be in G.P.: B^2 = A cdot C ### Core Logic Part 1: Coefficients of T_r, T_r+1, T_r+2 are binom12r-1, binom12r, binom12r+1. Since they are in G.P.: left[binom12rright]^2 = binom12r-1 cdot binom12r+1 fracbinom12rbinom12r-1 = fracbinom12r+1binom12r implies frac12-r+1r = frac12-rr+1 (13-r)(r+1) = r(12-r) implies 13r + 13 - r^2 - r = 12r - r^2 12r + 13 = 12r implies 13 = 0 quad (textNot possible) Thus, no real integer solution for r exists, so p = 0. ### Step 1: Calculate Rational Terms Sum q Part 2: Rational terms in expansion of (3^1/4 + 4^1/3)^12. General term: T_k+1 = binom12k (3^1/4)^12-k (4^1/3)^k = binom12k 3^frac12-k4 4^frack3 For the term to be rational, frac12-k4 and \frac{k}{3} must both be integers: - k must be a multiple of 3: k in \0, 3, 6, 9, 12\ - 12-k must be a multiple of 4, so k must be a multiple of 4: k in \0, 4, 8, 12\ The common values for k are k = 0 and k = 12. - At k = 0: T_1 = binom120 3^3 4^0 = 1 times 27 times 1 = 27 - At k = 12: T_13 = binom1212 3^0 4^4 = 1 times 1 times 256 = 256 Sum of rational terms q = 27 + 256 = 283. ### Step 2: Final Combination p + q = 0 + 283 = 283 ### Pattern Recognition To find common values for divisibility constraints, look for multiples of the least common multiple textlcm(3, 4) = 12 within the range [0, 12]. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Mathematics: Binomial Theorem
Q58 jee_main_2025_29_jan_morning Number of Integral Terms
The least value of n for which the number of integral terms in the Binomial expansion of left(sqrt[3]7 + sqrt[12]11right)^n is 183, is:
  • A. 2184
  • B. 2148
  • C. 2172
  • D. 2196

Solution

### Related Formula T_r+1 = binomnr a^n-r b^r ### Core Logic The general term in the expansion is: T_r+1 = binomnr (7)^fracn-r3 (11)^fracr12 For the term to be integral, both powers fracn-r3 and fracr12 must be integers. This dictates that r must be a multiple of 12 (r = 12k, where k is a non-negative integer). ### Step 1: Setup total count equation The values r can take are 0, 12, 24, dots, 12k. The total number of terms is given as 183. Since counting starts from k=0, the maximum value of k is: k_textmax = 183 - 1 = 182 ### Step 2: Calculate minimum n The maximum index value r required to achieve this count is: r_textmax = 12 times 182 = 2184 Hence, the least value of n must be 2184 to encompass all 183 integral terms. ### Pattern Recognition Number of terms formula when tracking steps of size L: textTotal Terms = lfloor fracnL rfloor + 1. Isolate n directly to compute bounds rapidly. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Mathematics: Binomial Theorem
Q23 jee_main_2024_01_february_morning General Term and Coefficients
If the Coefficient of x^30 in the expansion of left(1+frac1xright)^6(1+x^2)^7(1-x^3)^8, xne0 is alpha, then |alpha| equals
Numerical Answer. Answer: 678 to 678

Solution

### Related Formula General term in a binomial expansion (1+t)^n is given by: T_r+1 = binomnr t^r ### Core Logic Let's simplify the algebraic structure of the product expression first: left(1+frac1xright)^6(1+x^2)^7(1-x^3)^8 = frac(x+1)^6 (1+x^2)^7 (1-x^3)^8x^6 Finding the coefficient of x^30 in this full product is equivalent to finding the coefficient of x^36 in the numerator expansion: textTarget = textCoefficient of x^36 text in (1+x)^6 (1+x^2)^7 (1-x^3)^8 ### Step 1: Setting up General Term Constraints The product of the three general terms is: binom6r_1 x^r_1 cdot binom7r_2 (x^2)^r_2 cdot binom8r_3 (-x^3)^r_3 = binom6r_1binom7r_2binom8r_3 (-1)^r_3 x^r_1 + 2r_2 + 3r_3 We require the total exponent to equal 36: r_1 + 2r_2 + 3r_3 = 36 with boundaries 0 le r_1 le 6, 0 le r_2 le 7, 0 le r_3 le 8. ### Step 2: Case Analysis by r3 Let's evaluate non-vanishing integer combinations case-by-case: - **Case I: r_3 = 8** r_1 + 2r_2 = 36 - 24 = 12 - r_2 = 6, r_1 = 0 implies binom60binom76binom88(-1)^8 = 1 times 7 times 1 = 7 - r_2 = 5, r_1 = 2 implies binom62binom75binom88(-1)^8 = 15 times 21 times 1 = 315 - r_2 = 4, r_1 = 4 implies binom64binom74binom88(-1)^8 = 15 times 35 times 1 = 525 - r_2 = 3, r_1 = 6 implies binom66binom73binom88(-1)^8 = 1 times 35 times 1 = 35 - **Case II: r_3 = 7** r_1 + 2r_2 = 36 - 21 = 15 - r_2 = 7, r_1 = 1 implies binom61binom77binom87(-1)^7 = 6 times 1 times 8 times (-1) = -48 - r_2 = 6, r_1 = 3 implies binom63binom76binom87(-1)^7 = 20 times 7 times 8 times (-1) = -1120 - r_2 = 5, r_1 = 5 implies binom65binom75binom87(-1)^7 = 6 times 21 times 8 times (-1) = -1008 - **Case III: r_3 = 6** r_1 + 2r_2 = 36 - 18 = 18 - r_2 = 7, r_1 = 4 implies binom64binom77binom86(-1)^6 = 15 times 1 times 28 = 420 - r_2 = 6, r_1 = 6 implies binom66binom76binom86(-1)^6 = 1 times 7 times 28 = 196 ### Step 3: Summation for Alpha Summing all calculated values: alpha = (7 + 315 + 525 + 35) + (-48 - 1120 - 1008) + (420 + 196) alpha = 882 - 2176 + 616 = -678 Thus, the absolute value is: |alpha| = 678 ### Pattern Recognition Sees: Multi-product polynomial coefficient extraction problem. Trap: Remember that the negative sign inside (1-x^3)^8 alters the polarity of terms based on whether r_3 is odd or even. Always track the (-1)^r_3 factor carefully. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Mathematics: Binomial Theorem
Q28 jee_main_2024_29_january_evening Remainder and Divisibility Problems
Remainder when 64^32^32 is divided by 9 is equal to
Numerical Answer. Answer: 1 to 1

Solution

### Related Formula (9k + 1)^n equiv 1 pmod 9 ### Core Logic Let the giant power tower expression be variable parameter t = 32^32. Re-expressing baseline number base 64: 64 = 8^2 So, the total term evaluates to: 64^t = (8^2)^t = 8^2t ### Step 1: Evaluating Modulo Properties We can re-express baseline 8 as (9 - 1): 8^2t = (9 - 1)^2t Expanding this expression using the Binomial Theorem: (9 - 1)^2t = binom2t09^2t - dots + binom2t2t(-1)^2t Since the exponent 2t is an even number, (-1)^2t = 1. Therefore: (9 - 1)^2t = 9k + 1 equiv 1 pmod 9 Thus, the remainder obtained when divided by 9 is exactly 1. ### Pattern Recognition When evaluating exponents modulo M, reduce the base first. Since 64 equiv 1 pmod 9, any integer power of 64 trivially leaves a remainder of 1. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Mathematics: Binomial Theorem
Q1 jee_main_2024_27_jan_morning Properties of Binomial Coefficients
Given ^n-1C_r=(k^2-8)^nC_r+1, this holds true if and only if:
  • A. 2sqrt2 lt k le 3
  • B. 2sqrt3 lt k le 3sqrt2
  • C. 2sqrt3 lt k lt 3sqrt3
  • D. 2sqrt2 lt k lt 2sqrt3

Solution

### Related Formula frac^n-1C_r^nC_r+1 = fracr+1n ### Core Logic From the given equation: (k^2 - 8) = frac^n-1C_r^nC_r+1 Applying the combination property, we get: k^2 - 8 = fracr+1n Since n, r ge 0 and n ge r+1 for the combination to be valid, the ratio fracr+1n must satisfy: 0 < fracr+1n le 1 Substituting this bound into our expression: 0 < k^2 - 8 le 1 ### Step 1: Solving the Inequalities First inequality: k^2 - 8 > 0 Rightarrow k^2 > 8 Rightarrow k in (-infty, -2sqrt2) cup (2sqrt2, infty) Second inequality: k^2 - 8 le 1 Rightarrow k^2 - 9 le 0 Rightarrow k^2 le 9 Rightarrow -3 le k le 3 Taking the intersection of both intervals: k in [-3, -2sqrt2) cup (2sqrt2, 3] ### Step 2: Final Conclusion Looking at the options, we consider the positive domain interval: 2sqrt2 < k le 3 ### Pattern Recognition Combinatorics identities often reduce to bounds on variables. Memorize the ratio frac^n-1C_r^nC_r+1 = fracr+1n and use the strict combinatorial limit 0 < fracr+1n le 1 to form algebraic inequalities. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Maths: Binomial Theorem Class 11 Maths: Linear Inequalities

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