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We are given the piecewise function:
![\displaystyle \large{f(x) = \begin{cases} {x}^{3} \: \: (x < 0) \\ \sqrt[3]{x} \: \: (x > 0) \end{cases}}](https://tex.z-dn.net/?f=%20%5Cdisplaystyle%20%5Clarge%7Bf%28x%29%20%3D%20%20%5Cbegin%7Bcases%7D%20%20%7Bx%7D%5E%7B3%7D%20%20%5C%3A%20%20%5C%3A%20%28x%20%3C%200%29%20%5C%5C%20%20%5Csqrt%5B3%5D%7Bx%7D%20%20%5C%3A%20%20%5C%3A%20%28x%20%3E%200%29%20%5Cend%7Bcases%7D%7D)
To evaluate the value of function at x = -8 and x = 8, we know that -8 is less than 0 and 8 is greater than 0.
Therefore, if we want to evaluate the value of function at x = -8; we use the x^3 since it's given x < 0 for the function and for x = 8; we use the cube root of x since it's given x > 0.
Evaluate x = -8
From the piecewise function:
![\displaystyle \large{f(x) = \begin{cases} {x}^{3} \: \: (x < 0) \\ \sqrt[3]{x} \: \: (x > 0) \end{cases}}](https://tex.z-dn.net/?f=%20%5Cdisplaystyle%20%5Clarge%7Bf%28x%29%20%3D%20%20%5Cbegin%7Bcases%7D%20%20%7Bx%7D%5E%7B3%7D%20%20%5C%3A%20%20%5C%3A%20%28x%20%3C%200%29%20%5C%5C%20%20%5Csqrt%5B3%5D%7Bx%7D%20%20%5C%3A%20%20%5C%3A%20%28x%20%3E%200%29%20%5Cend%7Bcases%7D%7D)
Since -8 is less than 0, we use x^3.

Evaluate x = 8
From the piecewise function, since 8 is greater than 0, we use the cube root of x.
![\displaystyle \large{f(8) = \sqrt[3]{8} }](https://tex.z-dn.net/?f=%20%5Cdisplaystyle%20%5Clarge%7Bf%288%29%20%3D%20%20%5Csqrt%5B3%5D%7B8%7D%20%7D)
To evaluate the cube root, first we prime-factor the number.
![\displaystyle \large{f(8) = \sqrt[3]{2 \cdot 2 \cdot 2} }](https://tex.z-dn.net/?f=%20%5Cdisplaystyle%20%5Clarge%7Bf%288%29%20%3D%20%20%5Csqrt%5B3%5D%7B2%20%5Ccdot%202%20%5Ccdot%202%7D%20%7D)
Since it's a cube root, we pull three 2's out of the cube root and write only one 2.

Answer
Let me know if you have any questions!