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Let $$C_r$$ denote the binomial coefficient of $$x^r$$ in the expansion of $$(1 + x)^{10}$$. If for $$\alpha, \beta \in R$$,
$$C_{1} + 3 \cdot 2C_{2} + 5 \cdot 3C_{3} + \ldots $$ upto 10 terms $$= \frac{\alpha \times 2^{11}}{2^{\beta} - 1}(C_{0} + \frac{C_{1}}{2} + \frac{C_{2}}{3} + \ldots $$ upto 10 terms ) then the value of $$\alpha + \beta $$ is equal to ______.
Correct Answer: 286
Given,
$$C_r=\binom{10}{r}$$
Let
$$S=C_{1}+3\cdot2C_{2}+5\cdot3C_{3}+\cdots$$ upto $$10$$ terms
Now,
$$(1+x)^{10}=C_0+C_1x+C_2x^2+\cdots+C_{10}x^{10}$$
Differentiating,
$$10(1+x)^9=C_1+2C_2x+3C_3x^2+\cdots+10C_{10}x^9$$
Replace $$x$$ by $$x^2,$$
$$10(1+x^2)^9=C_1+2C_2x^2+3C_3x^4+\cdots+10C_{10}x^{18}$$
Multiplying by $$x,$$
$$10x(1+x^2)^9=C_1x+2C_2x^3+3C_3x^5+\cdots+10C_{10}x^{19}$$
Differentiating,
$$10\left((1+x^2)^9+x\cdot9(1+x^2)^8\cdot2x\right)=C_1+3\cdot2C_2x^2+5\cdot3C_3x^4+\cdots+19\cdot10C_{10}x^{18}$$
Putting $$x=1,$$
$$10\left(2^9+18\cdot2^8\right)=C_1+3\cdot2C_2+5\cdot3C_3+\cdots+19\cdot10C_{10}$$
Hence,
$$S=10\cdot2^8(2+18)$$
$$=10\cdot20\cdot2^8$$
$$=100\cdot2^9$$
Now,
$$T=C_0+\frac{C_1}{2}+\frac{C_2}{3}+\cdots+\frac{C_{10}}{11}$$
$$=\sum_{r=0}^{10}\frac{C_r}{r+1}$$
Since,
$$C_r=\binom{10}{r}$$
we use the identity
$$\frac1{r+1}\binom{10}{r}=\frac1{11}\binom{11}{r+1}$$
Therefore,
$$T=\frac1{11}\sum_{r=0}^{10}\binom{11}{r+1}$$
Now put
$$k=r+1$$
Then,
$$T=\frac1{11}\sum_{k=1}^{11}\binom{11}{k}$$
Using,
$$\sum_{k=0}^{11}\binom{11}{k}=2^{11}$$
we get
$$\sum_{k=1}^{11}\binom{11}{k}=2^{11}-1$$
Hence,
$$T=\frac{2^{11}-1}{11}$$
Previously,
$$S=C_1+3\cdot2C_2+5\cdot3C_3+\cdots+19\cdot10C_{10}=100\cdot2^9$$
Given,
$$S=\frac{\alpha\cdot2^{11}}{2^\beta-1}T$$
Substituting the values of $$S$$ and $$T,$$
$$100\cdot2^9=\frac{\alpha\cdot2^{11}}{2^\beta-1}\cdot\frac{2^{11}-1}{11}$$
Comparing denominator terms,
$$2^\beta-1=2^{11}-1$$
Hence,
$$\beta=11$$
Now,
$$100\cdot2^9=\frac{\alpha\cdot2^{11}}{11}$$
Dividing by $$2^9,$$
$$100=\frac{4\alpha}{11}$$
$$1100=4\alpha$$
$$\alpha=275$$
Therefore,
$$\alpha+\beta=275+11=286$$
Hence, $$\boxed{286}$$.
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