# (x^(-4/7))^7 what is the simplest form?

If I have marked-up the question correctly (I had to guess a bit), then the simplest form is either $\frac{1}{{x}^{4}}$ or ${x}^{- 4}$, depending on which you think is simpler.
When we raise an expression with an index to the power of another index, we multiply the indices, so ${\left({x}^{a}\right)}^{b} = {x}^{a \times b} = {x}^{a b}$.
In this case, ${\left({x}^{- \frac{4}{7}}\right)}^{7} = {x}^{\left(- \frac{4}{7} \times 7\right)} = {x}^{- 4}$.