(CESGRANRIO) O coeficiente de $\,x\,$ no desenvolvimento de $\phantom{X}(x\,+\,{\Large \frac{1}{2}})^{\large 21}\phantom{X}$ é:
a)
$\,{\large \frac{21}{\,2^{20}}}\,$
b)
$\,{\large \frac{1}{\,2^{20}}}\,$
c)
$\,{\large \frac{20!}{21}}\,$
e)
$\,{\large \frac{1}{2}}\,$
