Find the derivative of: 8sin2(7x3)\displaystyle {8}{{\sin}^{{2}}{\left({7}{x}^{{3}}\right)}}.

Hint: sin2(x)=[sin(x)]2\displaystyle {{\sin}^{{2}}{\left({x}\right)}}={\left[{\sin{{\left({x}\right)}}}\right]}^{{2}}...so use the chain rule (twice!).