- A$0$
- B$\;\left( {\begin{array}{*{20}{c}}{20}\\{10}\end{array}} \right)$
- C-$\;\left( {\begin{array}{*{20}{c}}{20}\\{10}\end{array}} \right)$
- ✓$\frac{1}{2}\left( {\begin{array}{*{20}{c}}{20}\\{10}\end{array}} \right)$
$\mathrm{x}^{2}+\ldots \ldots .20 \mathrm{C}_{10} \mathrm{c}_{10} \mathrm{x}^{10}+\ldots . .2 .20 \mathrm{C}_{20} \mathrm{x}^{20}$
Put $\mathrm{x}=-1 .(0)= ^{20} \mathrm{C}_{0}- ^{20} \mathrm{C}_{1}+ ^{20} \mathrm{C}_{2}- ^{20} \mathrm{C}_{3}+$$\ldots . .+ ^{20} \mathrm{C}_{10}- ^{20} \mathrm{C}_{11} \ldots+^{20} \mathrm{C}_{20}$
$0=2[^{20} \mathrm{C}_{0}- ^{20} \mathrm{C}_{1}+ ^{20} \mathrm{C}_{2}- ^{20} $$\mathrm{C}_{3}+\ldots . .- ^{20} \mathrm{C}_{9} ]+ ^{20} \mathrm{C}_{10}$
$^{20} \mathrm{C}_{10}=2 [^{20} \mathrm{C}_{0}-^{20} \mathrm{C}_{1}$$+ ^{20} \mathrm{C}_{2}-^{20} \mathrm{C}_{3}+\ldots \ldots-^{20} \mathrm{C}_{9}+^{20} \mathrm{C}_{10}]$
$^{20} \mathrm{C}_{0}-^{20} \mathrm{C}_{1}+^{20} \mathrm{C}_{2}-^{20} \mathrm{C}_{3} \cdot \ldots .$ i" $^{2 \mathrm{n}} \mathrm{C}_{10}$
$=\frac{1}{2}^{20} \mathrm{C}_{10}$
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