f(n) = 5n^3-1

y = 5n3-1 (to find inverse equate the equation to y)

y+1 = 5n3 (add 1 to both sides of equation)

(y+1)/5 = n3 (divide by 5 on both sides of equation)

((y+1)/5)1/3 = n (do cube root on both sides of equation)

So, f-1(n) = ((n+1)/5)1/3 (substitute y to n) to get the final answer)

This is the shortest way to find inverse