0\; ,\\\\sinx=\frac{a-1}{a+3}\; \; ,\; \; a\ne -3\; ,\\\\-1\leq \frac{a-1}{a+3}\leq 1\; \; \Rightarrow \; \; \left \{ {{\frac{a-1}{a+3}\leq 1} \atop {\frac{a-1}{a+3}\geq -1}} \right. \; \; \left \{ {{\frac{a-1-a-3}{a+3}\leq 0} \atop {\frac{a-1+a+3}{a+3}\geq 0}} \right. \; \left \{ {{\frac{-2}{a+3}\leq 0} \atop {\frac{2(a+1)}{a+3}\geq 0}} \right. \\\\\left \{ {{a+3\geq 0} \atop {a\in (-\infty ,-3)\cup (-1,+\infty )}} \right. \; \left \{ {{a\geq 0\; \; ,\; \; a>0} \atop {a\in (-\infty ,-3)\cup (-1,+\infty )}} \right. \; \Rightarrow \; \; a\in (0,+\infty )" alt="2)\; \; (a+3)\cdot sinx=a-1\; ,\; \; a>0\; ,\\\\sinx=\frac{a-1}{a+3}\; \; ,\; \; a\ne -3\; ,\\\\-1\leq \frac{a-1}{a+3}\leq 1\; \; \Rightarrow \; \; \left \{ {{\frac{a-1}{a+3}\leq 1} \atop {\frac{a-1}{a+3}\geq -1}} \right. \; \; \left \{ {{\frac{a-1-a-3}{a+3}\leq 0} \atop {\frac{a-1+a+3}{a+3}\geq 0}} \right. \; \left \{ {{\frac{-2}{a+3}\leq 0} \atop {\frac{2(a+1)}{a+3}\geq 0}} \right. \\\\\left \{ {{a+3\geq 0} \atop {a\in (-\infty ,-3)\cup (-1,+\infty )}} \right. \; \left \{ {{a\geq 0\; \; ,\; \; a>0} \atop {a\in (-\infty ,-3)\cup (-1,+\infty )}} \right. \; \Rightarrow \; \; a\in (0,+\infty )" align="absmiddle" class="latex-formula">