The function which reverses into another function is called an inverse function.
From the given data in the question, we have y = 2x² - 8
To find the inverse of any function we need to interchange the variables.
Hence, we get x = 2y² - 8
⇒ x = 2y² - 8
⇒ x + 8 = 2y²
⇒ (x + 8) / 2 = y²
⇒ √[(x + 8) / 2] = y
Therefore, √[(x + 8) / 2] is the inverse of y = 2x² - 8.