The convert/tan function converts all trigonometric functions appearing in the expression to tan.

$f≔\sin \left(x\right)\cos \left(x\right)$

$f≔\sin \left(x\right)\cos \left(x\right)$

$\mathrm{convert}\left(f\,\tan \right)$

$\frac{2\tan \left(\frac{x}{2}\right)\left(1-{\tan \left(\frac{x}{2}\right)}^2\right)}{{\left(1+{\tan \left(\frac{x}{2}\right)}^2\right)}^2}$