Solution & Explanation
### Related Formula
General term of binomial expansion (x + y)^n$(x + y)^n$:
T_k+1 = binomnk x^n-k y^k$$T_{k+1} = \binom{n}{k} x^{n-k} y^k$$
Condition for three terms A, B, C$A, B, C$ to be in G.P.:
B^2 = A cdot C$B^2 = A \cdot C$
### Core Logic
Part 1: Coefficients of T_r, T_r+1, T_r+2$T_r, T_{r+1}, T_{r+2}$ are binom12r-1, binom12r, binom12r+1$\binom{12}{r-1}, \binom{12}{r}, \binom{12}{r+1}$.
Since they are in G.P.:
left[binom12rright]^2 = binom12r-1 cdot binom12r+1$$\left[\binom{12}{r}\right]^2 = \binom{12}{r-1} \cdot \binom{12}{r+1}$$
fracbinom12rbinom12r-1 = fracbinom12r+1binom12r implies frac12-r+1r = frac12-rr+1$$\frac{\binom{12}{r}}{\binom{12}{r-1}} = \frac{\binom{12}{r+1}}{\binom{12}{r}} \implies \frac{12-r+1}{r} = \frac{12-r}{r+1}$$
(13-r)(r+1) = r(12-r) implies 13r + 13 - r^2 - r = 12r - r^2$$(13-r)(r+1) = r(12-r) \implies 13r + 13 - r^2 - r = 12r - r^2$$
12r + 13 = 12r implies 13 = 0 quad (textNot possible)$$12r + 13 = 12r \implies 13 = 0 \quad (\text{Not possible})$$
Thus, no real integer solution for r$r$ exists, so p = 0$p = 0$.
### Step 1: Calculate Rational Terms Sum q
Part 2: Rational terms in expansion of (3^1/4 + 4^1/3)^12$(3^{1/4} + 4^{1/3})^{12}$.
General term:
T_k+1 = binom12k (3^1/4)^12-k (4^1/3)^k = binom12k 3^frac12-k4 4^frack3$$T_{k+1} = \binom{12}{k} (3^{1/4})^{12-k} (4^{1/3})^k = \binom{12}{k} 3^{\frac{12-k}{4}} 4^{\frac{k}{3}}$$
For the term to be rational, frac12-k4$\frac{12-k}{4}$ and \frac{k}{3} must both be integers:
- k$k$ must be a multiple of 3: k in \0, 3, 6, 9, 12\$k \in \{0, 3, 6, 9, 12\}$
- 12-k$12-k$ must be a multiple of 4, so k$k$ must be a multiple of 4: k in \0, 4, 8, 12\$k \in \{0, 4, 8, 12\}$
The common values for k$k$ are k = 0$k = 0$ and k = 12$k = 12$.
- At k = 0$k = 0$:
T_1 = binom120 3^3 4^0 = 1 times 27 times 1 = 27$$T_1 = \binom{12}{0} 3^3 4^0 = 1 \times 27 \times 1 = 27$$
- At k = 12$k = 12$:
T_13 = binom1212 3^0 4^4 = 1 times 1 times 256 = 256$$T_{13} = \binom{12}{12} 3^0 4^4 = 1 \times 1 \times 256 = 256$$
Sum of rational terms q = 27 + 256 = 283$q = 27 + 256 = 283$.
### Step 2: Final Combination
p + q = 0 + 283 = 283$$p + q = 0 + 283 = 283$$
### Pattern Recognition
To find common values for divisibility constraints, look for multiples of the least common multiple textlcm(3, 4) = 12$\text{\lcm}(3, 4) = 12$ within the range [0, 12]$[0, 12]$.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Mathematics: Binomial Theorem
More Binomial Theorem Previous-Year Questions
Q16
jee_main_2026_21_jan_morning
Coefficients in Binomial Expansions
If the
coefficient of x in the expansion of
(ax^2 + bx + c)(1 - 2x)^26$(ax^{2} + bx + c)(1 - 2x)^{26}$ is -56 and the coefficients of
x^2$x^{2}$ and
x^3$x^{3}$ are both zero, then
a + b + c$a + b + c$ is equal to
- A. 1300
- B. 1500
- C. 1403
- D. 1483
Solution
### Related Formula
(1 - 2x)^26 = sum_r=0^26 binom26r (-2x)^r$$(1 - 2x)^{26} = \sum_{r=0}^{26} \binom{26}{r} (-2x)^r$$
The coefficient extraction utilizes the distributive property over the polynomial (ax^2+bx+c)$(ax^2+bx+c)$.
### Core Logic
Expansion of expression: (ax^2 + bx + c) sum_r=0^26 binom26r (-2x)^r$(ax^{2} + bx + c) \sum_{r=0}^{26} \binom{26}{r} (-2x)^{r}$
For the term in x^2$x^2$, we pick contributions yielding total power 2:
a cdot (x^0 text term of sum) + b cdot (x^1 text term) + c cdot (x^2 text term) = 0$a \cdot (x^0 \text{ term of sum}) + b \cdot (x^1 \text{ term}) + c \cdot (x^2 \text{ term}) = 0$
a cdot binom260(-2)^0 + b cdot binom261(-2)^1 + c cdot binom262(-2)^2 = 0$a \cdot \binom{26}{0}(-2)^0 + b \cdot \binom{26}{1}(-2)^1 + c \cdot \binom{26}{2}(-2)^2 = 0$
a - 52b + 1300c = 0 dots(1)$a - 52b + 1300c = 0 \dots(1)$
### Step 1: Formulate the system of linear equations
For the term in x^3$x^3$ (set to 0):
a cdot (x^1 text term) + b cdot (x^2 text term) + c cdot (x^3 text term) = 0$a \cdot (x^1 \text{ term}) + b \cdot (x^2 \text{ term}) + c \cdot (x^3 \text{ term}) = 0$
a cdot binom261(-2)^1 + b cdot binom262(-2)^2 + c cdot binom263(-2)^3 = 0$a \cdot \binom{26}{1}(-2)^1 + b \cdot \binom{26}{2}(-2)^2 + c \cdot \binom{26}{3}(-2)^3 = 0$
-52a + 1300b - 20800c = 0 dots(2)$-52a + 1300b - 20800c = 0 \dots(2)$
For the term in x^1$x^1$ (set to -56):
b cdot (x^0 text term) + c cdot (x^1 text term) = -56$b \cdot (x^0 \text{ term}) + c \cdot (x^1 \text{ term}) = -56$
b cdot binom260(-2)^0 + c cdot binom261(-2)^1 = -56$b \cdot \binom{26}{0}(-2)^0 + c \cdot \binom{26}{1}(-2)^1 = -56$
b - 52c = -56 dots(3)$b - 52c = -56 \dots(3)$
### Step 2: Solve the Linear System
From (3), b = 52c - 56$b = 52c - 56$.
Substitute into (2) divided by -52$-52$ to simplify: a - 25b + 400c = 0$a - 25b + 400c = 0$.
Substitute into (1): a - 52b + 1300c = 0$a - 52b + 1300c = 0$.
Subtracting: 27b - 900c = 0 Rightarrow b = frac1003c$27b - 900c = 0 \Rightarrow b = \frac{100}{3}c$.
Wait, recalculating directly:
From (2): -52a + 1300b - 20800c = 0 Rightarrow a - 25b + 400c = 0$-52a + 1300b - 20800c = 0 \Rightarrow a - 25b + 400c = 0$.
From (1): a - 52b + 1300c = 0$a - 52b + 1300c = 0$.
(a - 25b + 400c) - (a - 52b + 1300c) = 0 Rightarrow 27b - 900c = 0 Rightarrow 3b = 100c$ (a - 25b + 400c) - (a - 52b + 1300c) = 0 \Rightarrow 27b - 900c = 0 \Rightarrow 3b = 100c$.
Substitute into (3): b - 52(3b/100) = -56 Rightarrow$b - 52(3b/100) = -56 \Rightarrow$ fractional results? Let's check coefficients accurately.
binom263(-2)^3 = frac26 cdot 25 cdot 246 times (-8) = 2600 times -8 = -20800$\binom{26}{3}(-2)^3 = \frac{26 \cdot 25 \cdot 24}{6} \times (-8) = 2600 \times -8 = -20800$.
Divide by -52: a - 25b + 400c = 0$a - 25b + 400c = 0$. Correct.
(a - 52b + 1300c) - (a - 25b + 400c) = -27b + 900c = 0 Rightarrow 27b = 900c Rightarrow b = frac1003c$(a - 52b + 1300c) - (a - 25b + 400c) = -27b + 900c = 0 \Rightarrow 27b = 900c \Rightarrow b = \frac{100}{3}c$.
This contradicts integer expectations. Let's substitute b$b$ from (3) directly.
b = 52c - 56$b = 52c - 56$.
27(52c - 56) = 900c$27(52c - 56) = 900c$
1404c - 1512 = 900c Rightarrow 504c = 1512 Rightarrow c = 3$1404c - 1512 = 900c \Rightarrow 504c = 1512 \Rightarrow c = 3$.
Then b = 52(3) - 56 = 156 - 56 = 100$b = 52(3) - 56 = 156 - 56 = 100$.
From (1): a - 52(100) + 1300(3) = 0 Rightarrow a - 5200 + 3900 = 0 Rightarrow a = 1300$a - 52(100) + 1300(3) = 0 \Rightarrow a - 5200 + 3900 = 0 \Rightarrow a = 1300$.
### Step 3: Compute final value
We have a = 1300$a = 1300$, b = 100$b = 100$, c = 3$c = 3$.
a + b + c = 1300 + 100 + 3 = 1403$$a + b + c = 1300 + 100 + 3 = 1403$$
### Pattern Recognition
Polynomial-Binomial product coefficient extractions strictly generate cascaded linear Diophantine-style equations. Solving from the lowest degree constraint (x^1$x^1$) upward sequentially unwinds the system cleanly.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Maths: Binomial Theorem
Q65
jee_main_2025_02_april_evening
Properties of Binomial Coefficients
If sum_mathrmr = 0^10left(frac10^mathrmr + 1 - 110^mathrmrright) cdot binom11r + 1 = fracalpha^11 - 11^1110^10$\sum_{\mathrm{r} = 0}^{10}\left(\frac{10^{\mathrm{r} + 1} - 1}{10^{\mathrm{r}}}\right) \cdot \binom{11}{r + 1} = \frac{\alpha^{11} - 11^{11}}{10^{10}}$, then alpha$\alpha$ is equal to:
Solution
### Related Formula
textSum of binomial coefficients: sum_k=0^n binomnk x^k = (1 + x)^n$$\text{Sum of binomial coefficients: } \sum_{k=0}^{n} \binom{n}{k} x^k = (1 + x)^n$$
textShifted binomial sum: sum_k=1^n binomnk x^k = (1+x)^n - 1$$\text{Shifted binomial sum: } \sum_{k=1}^{n} \binom{n}{k} x^k = (1+x)^n - 1$$
### Core Logic
We split the summation into two parts, express each as a binomial series expansion, and equate the resulting algebraic fraction to solve for alpha$\alpha$.
### Step 1: Split the summation
The general term inside the summation can be written as:
left( frac10^r+1 - 110^r right) = 10 - frac110^r = 10 - 10 left( frac110 right)^r+1$$\left( \frac{10^{r+1} - 1}{10^r} \right) = 10 - \frac{1}{10^r} = 10 - 10 \left( \frac{1}{10} \right)^{r+1}$$
Substitute this back into the sum:
S = sum_r=0^10 left[ 10 - 10 left( frac110 right)^r+1 right] binom11r+1$$S = \sum_{r=0}^{10} \left[ 10 - 10 \left( \frac{1}{10} \right)^{r+1} \right] \binom{11}{r+1}$$
S = 10 sum_r=0^10 binom11r+1 - 10 sum_r=0^10 binom11r+1 left( frac110 right)^r+1$$S = 10 \sum_{r=0}^{10} \binom{11}{r+1} - 10 \sum_{r=0}^{10} \binom{11}{r+1} \left( \frac{1}{10} \right)^{r+1}$$
### Step 2: Evaluate both parts of the sum
For the first part, let s = r+1$s = r+1$:
sum_r=0^10 binom11r+1 = sum_s=1^11 binom11s = 2^11 - 1$$\sum_{r=0}^{10} \binom{11}{r+1} = \sum_{s=1}^{11} \binom{11}{s} = 2^{11} - 1$$
For the second part, using s = r+1$s = r+1$:
sum_r=0^10 binom11r+1 left( frac110 right)^r+1 = sum_s=1^11 binom11s left( frac110 right)^s = left( 1 + frac110 right)^11 - 1 = left( frac1110 right)^11 - 1$$\sum_{r=0}^{10} \binom{11}{r+1} \left( \frac{1}{10} \right)^{r+1} = \sum_{s=1}^{11} \binom{11}{s} \left( \frac{1}{10} \right)^s = \left( 1 + \frac{1}{10} \right)^{11} - 1 = \left( \frac{11}{10} \right)^{11} - 1$$
### Step 3: Combine and find alpha
Multiply both parts by 10:
S = 10 left( 2^11 - 1 right) - 10 left[ left( frac1110 right)^11 - 1 right]$$S = 10 \left( 2^{11} - 1 \right) - 10 \left[ \left( \frac{11}{10} \right)^{11} - 1 \right]$$
S = 10 cdot 2^11 - 10 - 10 cdot frac11^1110^11 + 10 = 10 cdot 2^11 - frac11^1110^10$$S = 10 \cdot 2^{11} - 10 - 10 \cdot \frac{11^{11}}{10^{11}} + 10 = 10 \cdot 2^{11} - \frac{11^{11}}{10^{10}}$$
Express the first term with a denominator of 10^10$10^{10}$:
10 cdot 2^11 = frac10^11 cdot 2^1110^10 = frac20^1110^10$$10 \cdot 2^{11} = \frac{10^{11} \cdot 2^{11}}{10^{10}} = \frac{20^{11}}{10^{10}}$$
Thus, the total sum is:
S = frac20^11 - 11^1110^10$$S = \frac{20^{11} - 11^{11}}{10^{10}}$$
Comparing this with fracalpha^11 - 11^1110^10$\frac{\alpha^{11} - 11^{11}}{10^{10}}$, we find:
alpha = 20$\alpha = 20$
### Pattern Recognition
Binomial base scaling: Whenever you see a sum of the form sum a^r binomnr$\sum a^r \binom{n}{r}$, it is simply the expanded form of a shifted binomial expansion of (1 + a)^n$(1 + a)^n$. Factoring out scaling constants yields standard analytical forms.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Mathematics: Binomial Theorem
Q
jee_main_2025_02_april_morning
Term Independent of x
The term independent of x$x$ in the expansion of left(frac (x + 1)(x ^ frac 23 + 1 - x ^ frac 13) - frac (x - 1)(x - x ^ frac 12)right) ^ 1 0, x > 1$\left(\frac {(x + 1)}{(x ^ {\frac {2}{3}} + 1 - x ^ {\frac {1}{3}})} - \frac {(x - 1)}{(x - x ^ {\frac {1}{2}})}\right) ^ {1 0}, x > 1$ is:
- A. 210$210$
- B. 150$150$
- C. 240$240$
- D. 120$120$
Solution
### Related Formula
Algebraic factorizations:
x+1 = left(x^1/3right)^3 + 1^3 = left(x^1/3+1right)left(x^2/3-x^1/3+1right)$$x+1 = \left(x^{1/3}\right)^3 + 1^3 = \left(x^{1/3}+1\right)\left(x^{2/3}-x^{1/3}+1\right)$$
x-1 = left(sqrtxright)^2 - 1^2 = (sqrtx-1)(sqrtx+1)$$x-1 = \left(\sqrt{x}\right)^2 - 1^2 = (\sqrt{x}-1)(\sqrt{x}+1)$$
### Core Logic
Simplify inside the parentheses before using the Binomial general term formula.
### Step 1: Simplify Bracket Terms
First fraction:
fracx+1x^2/3-x^1/3+1 = x^1/3+1$$\frac{x+1}{x^{2/3}-x^{1/3}+1} = x^{1/3}+1$$
Second fraction:
fracx-1x-x^1/2 = frac(sqrtx-1)(sqrtx+1)sqrtx(sqrtx-1) = fracsqrtx+1sqrtx = 1 + x^-1/2$$\frac{x-1}{x-x^{1/2}} = \frac{(\sqrt{x}-1)(\sqrt{x}+1)}{\sqrt{x}(\sqrt{x}-1)} = \frac{\sqrt{x}+1}{\sqrt{x}} = 1 + x^{-1/2}$$
Subtract the two simplified results:
left(x^1/3+1right) - left(1+x^-1/2right) = x^1/3 - x^-1/2$$\left(x^{1/3}+1\right) - \left(1+x^{-1/2}\right) = x^{1/3} - x^{-1/2}$$
### Step 2: Apply Binomial Theorem
The expression simplifies to left(x^1/3 - x^-1/2right)^10$\left(x^{1/3} - x^{-1/2}\right)^{10}$. Write the general term T_r+1$T_{r+1}$:
T_r+1 = binom10r left(x^1/3right)^10-r left(-x^-1/2right)^r = binom10r (-1)^r x^frac10-r3 - fracr2$$T_{r+1} = \binom{10}{r} \left(x^{1/3}\right)^{10-r} \left(-x^{-1/2}\right)^r = \binom{10}{r} (-1)^r x^{\frac{10-r}{3} - \frac{r}{2}}$$
### Step 3: Solve for Independent Term
Set the net power of x$x$ to zero:
frac10-r3 - fracr2 = 0 implies 20 - 2r - 3r = 0 implies 5r = 20 implies r = 4$$\frac{10-r}{3} - \frac{r}{2} = 0 \implies 20 - 2r - 3r = 0 \implies 5r = 20 \implies r = 4$$
Substitute r=4$r=4$ into the general term expression:
textCoefficient = binom104 (-1)^4 = frac10 times 9 times 8 times 74 times 3 times 2 times 1 = 210$$\text{Coefficient} = \binom{10}{4} (-1)^4 = \frac{10 \times 9 \times 8 \times 7}{4 \times 3 \times 2 \times 1} = 210$$
### Pattern Recognition
The initial fractions look complex but contain simple hidden identities (a^3+b^3$a^3+b^3$ and a^2-b^2$a^2-b^2$). Identifying these transforms a daunting fraction expansion into a classic two-term independent coefficient puzzle.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Mathematics: Binomial Theorem
Q72
jee_main_2025_03_april_evening
Trinomial Expansion
Let (1 + x + x^2)^10 = a_0 + a_1x + a_2x^2 + dots + a_20x^20$(1 + x + x^2)^{10} = a_0 + a_1x + a_2x^2 + \dots + a_{20}x^{20}$. If (a_1 + a_3 + a_5 + dots + a_19) - 11a_2 = 121k$(a_1 + a_3 + a_5 + \dots + a_{19}) - 11a_2 = 121k$, then k$k$ is equal to
Numerical Answer. Answer: 239 to 239
Solution
### Related Formula
For trinomial expansion:
(1+x+x^2)^n = sum_r=0^2n a_r x^r$$(1+x+x^2)^n = \sum_{r=0}^{2n} a_r x^r$$
Symmetric coefficients can be extracted by substituting x=1$x=1$ and x=-1$x=-1$.
### Core Logic
Let's perform the substitution:
- For x = 1$x = 1$:
3^10 = a_0 + a_1 + a_2 + dots + a_20 quad text--- (1)$$3^{10} = a_0 + a_1 + a_2 + \dots + a_{20} \quad \text{--- (1)}$$
- For x = -1$x = -1$:
1^10 = a_0 - a_1 + a_2 - a_3 + dots + a_20 quad text--- (2)$$1^{10} = a_0 - a_1 + a_2 - a_3 + \dots + a_{20} \quad \text{--- (2)}$$
### Step 1: Extracting odd term sum
Subtracting (2) from (1):
3^10 - 1 = 2(a_1 + a_3 + a_5 + dots + a_19)$$3^{10} - 1 = 2(a_1 + a_3 + a_5 + \dots + a_{19})$$
a_1 + a_3 + a_5 + dots + a_19 = frac3^10 - 12$$a_1 + a_3 + a_5 + \dots + a_{19} = \frac{3^{10} - 1}{2}$$
Since 3^5 = 243 implies 3^10 = 59049$3^5 = 243 \implies 3^{10} = 59049$:
a_1 + a_3 + a_5 + dots + a_19 = frac59049 - 12 = 29524$$a_1 + a_3 + a_5 + \dots + a_{19} = \frac{59049 - 1}{2} = 29524$$
### Step 2: Finding a_2$a_2$ and k$k$
Using expansion formula to find a_2$a_2$ (coefficient of x^2$x^2$):
(1 + x + x^2)^10 = sum frac10!p! q! r! x^q + 2r quad (p+q+r = 10)$$(1 + x + x^2)^{10} = \sum \frac{10!}{p! q! r!} x^{q + 2r} \quad (p+q+r = 10)$$
For q + 2r = 2$q + 2r = 2$:
- Case 1: r=1, q=0 implies p=9$r=1, q=0 \implies p=9$. Coefficient = frac10!9! 0! 1! = 10$\frac{10!}{9! 0! 1!} = 10$
- Case 2: r=0, q=2 implies p=8$r=0, q=2 \implies p=8$. Coefficient = frac10!8! 2! 0! = 45$\frac{10!}{8! 2! 0!} = 45$
a_2 = 10 + 45 = 55$$a_2 = 10 + 45 = 55$$
Now substitute into the target relation:
29524 - 11(55) = 29524 - 605 = 28919$$29524 - 11(55) = 29524 - 605 = 28919$$
121k = 28919 implies k = 239$$121k = 28919 \implies k = 239$$
### Pattern Recognition
Substituting standard complex roots or positive units is the fastest way to resolve sum of subset coefficients in polynomial expansions. Always use partition calculations for the early index terms (a_1, a_2$a_1, a_2$) rather than standard multinomial permutations to avoid calculation mistakes.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Mathematics: Binomial Theorem
Q54
jee_main_2025_07_april_morning
Remainder Problems
The remainder when left((64)^(64)right)^(64)$\left((64)^{(64)}\right)^{(64)}$ is divided by 7 is equal to
- A. 4$4$
- B. 1$1$
- C. 3$3$
- D. 6$6$
Solution
### Related Formula
Binomial expansion for checking remainders:
(1 + kx)^n = 1 + n(kx) + fracn(n-1)2(kx)^2 + dots equiv 1 pmod x$$(1 + kx)^n = 1 + n(kx) + \frac{n(n-1)}{2}(kx)^2 + \dots \equiv 1 \pmod x$$
### Core Logic
Let the target expression be N = left((64)^64right)^64$N = \left((64)^{64}\right)^{64}$.
Using power rules, N = 64^64 times 64 = 64^64^2$N = 64^{64 \times 64} = 64^{64^2}$.
Let the large exponent exponent be n = 64^2$n = 64^2$.
We need to find the remainder of 64^n$64^n$ when divided by 7$7$.
### Step 1: Express Base in Terms of Modulus
Observe that 64 = 63 + 1 = 7 times 9 + 1$64 = 63 + 1 = 7 \times 9 + 1$.
Substituting this into the expression:
N = (1 + 63)^n$N = (1 + 63)^n$
Expanding using the binomial theorem:
N = 1 + ^nC_1(63) + ^nC_2(63)^2 + dots + ^nC_n(63)^n$$N = 1 + ^nC_1(63) + ^nC_2(63)^2 + \dots + ^nC_n(63)^n$$
N = 1 + 63 cdot lambda = 1 + 7(9lambda)$$N = 1 + 63 \cdot \lambda = 1 + 7(9\lambda)$$
Since 7(9lambda)$7(9\lambda)$ is perfectly divisible by 7$7$, the remaining term is 1$1$.
### Pattern Recognition
Whenever the base can be written as km + 1$km + 1$, where m$m$ is the divisor, the value of (km + 1)^n equiv 1^n equiv 1 pmod m$(km + 1)^n \equiv 1^n \equiv 1 \pmod m$ instantly, regardless of the size or complexity of the exponent layout.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Mathematics: Binomial Theorem