\(\displaystyle{\frac{{{2}{\sin{{\left({x}\right)}}}{\cos{{\left({x}\right)}}}}}{{{{\cos}^{{4}}{\left({x}\right)}}}}}={2}\cdot{\frac{{{\sin{{\left({x}\right)}}}}}{{{\cos{{\left({x}\right)}}}}}}\cdot{\frac{{{1}}}{{{{\cos}^{{2}}{\left({x}\right)}}}}}={2}{\tan{{\left({x}\right)}}}{{\sec}^{{2}}{\left({x}\right)}}\)