Answer :
Hello,
[tex]f(x)=2x^7=-1\\ ==\ \textgreater \ x= \sqrt7]{ -\frac{1}{2}} \\ ==\ \textgreater \ x=-\sqrt7]{-\frac{1}{2}}\\ ==\ \textgreater \ x=0,9057236642639066715941728732151...\\. [/tex]
[tex]f(x)=2x^7=-1\\ ==\ \textgreater \ x= \sqrt7]{ -\frac{1}{2}} \\ ==\ \textgreater \ x=-\sqrt7]{-\frac{1}{2}}\\ ==\ \textgreater \ x=0,9057236642639066715941728732151...\\. [/tex]