Use part 2 of the Fundamental Theorem of Calculus to find the derivative of
F(x)=x3xcos(t4)dt\displaystyle {F}{\left({x}\right)}={\int_{{{x}}}^{{{3}{x}}}}{\cos{{\left({t}^{{{4}}}\right)}}}{\left.{d}{t}\right.}.

F(x)\displaystyle {F}'{\left({x}\right)} =