Sendo $\;k\,\in\,\mathbb{Z}\;$, calcule, em cada caso, o valor de $\,sen\,x\,$, com:
a)
$\,x\,=\,(2k\,+\,1)\,\centerdot\,\pi\,$
b)
$\,x\,=\,(2k\,+\,1)\dfrac{\,\pi\,}{2}\,$
c)
$\,x\,=\,\dfrac{\,\pi\,}{4}\,+\,k\pi\,$
d)
$\,x\,=\,-\dfrac{\,\pi\,}{3}\,+\,2k\pi\,$ ou $\,x\,=\,-\dfrac{\,2\pi\,}{3}\,+\,2k\pi\,$