In this problem , I have to find the third derivative of the fourth root of 2x cubed minus 16. so Third derivative of (fourth root) 4 2x^3 - 16 Solution The fourth root can be thought of as (2x^3) being raised to the 1/4 power so you can just multiply the power and get 2x^3/4 - 16 Take the first derivative: 3/4*2x^-1/4 Second derivative: 3/4*-1/4*2x^-5/4 = -3/16*2x^-5/4 Third derivative: -3/16*-5/4*2x^-9/4 = 15/64*(2x^-9/4).