Exercício sobre trigonometria

(MAPOFEI - 1976) Resolver o sistema $\,\left\{\begin{array}{rcr} sen\,(x\,+\,y)\,=\,0 & \\ x\,-\,y\,=\,\pi \phantom{XXX} & \\ \end{array} \right.\,$

resposta: $\,x\,=\,\frac{\pi}{2}\,+\,\frac{k\pi}{2}\,$, $\,y\,=\,-\frac{\pi}{2}\,+\,\frac{k\pi}{2}\,$
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