$\displaystyle {f{{\left({x}\right)}}}=\sqrt{{{343}{x}^{{4}}+{147}{x}^{{3}}+{21}{x}^{{2}}+{1}{x}}}$
Use the chain rule or the graph to find the points where the derivative of f does not exist.

Enter your answer as a list in numerical order enclosed with {} with a comma separating adjacent numbers.