Question
The sum $$\frac{1}{2}{\,^{10}}{C_0} - {\,^{10}}{C_1} + 2 \cdot {\,^{10}}{C_2} - {2^2} \cdot {\,^{10}}{C_3} + ..... + {2^9} \cdot {\,^{10}}{C_{10}}$$ is equal to
A.
$$\frac{1}{2}$$
B.
$$0$$
C.
$$\frac{1}{2} \cdot {3^{10}}$$
D.
None of these
Answer :
$$\frac{1}{2}$$
Solution :
Sum $$ = \frac{1}{2}\,\left\{ {^{10}{C_0} - {\,^{10}}{C_1} \cdot 2 + {\,^{10}}{C_2} \cdot {2^2} - {\,^{10}}{C_3} \cdot {2^3} + ..... + {\,^{10}}{C_{10}} \cdot {2^{10}}} \right\}$$
$$\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \frac{1}{2}{\left( {1 - 2} \right)^{10}} = \frac{1}{2}.$$