One has $$f(x) = \frac{\sin(x)}{x} = \int_0^1 \cos(x t)\,d t$$ hence $$ \left|f^\prime(x)\right| = \left |\int_0^1 t \sin(x t)\,dt\right | \le\int_0^1t\,d t \le \frac{1}{2} $$ hence $$\forall x, y\quad |f(x) - f(y)| \le \frac{1}{2}|x-y|$$
One has $$f(x) = \frac{\sin(x)}{x} = \int_0^1 \cos(x t)\,d t$$ hence $$ \left|f^\prime(x)\right| = \left |\int_0^1 t \sin(x t)\,dt\right | \le\int_0^1t\,d t \le \frac{1}{2} $$ hence $$\forall x, y\quad |f(x) - f(y)| \le \frac{1}{2}|x-y|$$