This is LaTeX code:
[latex]
f(-x) = \frac{\sin -x}{-x} \cdot \frac1{(-x)^2+1} = \frac{-\sin x}{-x} \cdot \frac1{x^2+1} = \frac{\sin x}x \cdot \frac1{x^2+1} = f(x)
[/latex]