\\ a\leq5, a\geq-5\\ " alt="3\sin x-4\cos x\leq a\ , \sqrt{3^2+(-4)^2}=5;\\ \frac{3}{5}\sin x-\frac{4}{5}\cos x\leq\frac{a}{5}\\ \cos \phi=\frac{3}{5}; \ \sin \phi=\frac{4}{5}\\ \sin x\cos \phi - \sin \phi \cos x\leq\frac{a}{5}\\ \sin (x-\phi)\leq\frac{a}{5}\\ |\frac{a}{5}|\leq1\ =>\\ a\leq5, a\geq-5\\ " align="absmiddle" class="latex-formula">
Ответ: [-5;5]