if f(x) = (x^5-1)/3, find f^-1(-31/96)

(x^5-1)/3, find f^-1(-31/96)

Write  

y = (x^5-1)/3       

3y  = x^5 - 1

3y + 1  =  x^5

(3y + 1)^(1/5)  = x        swap x and y

(3x + 1 )^(1/5)  = y  = f^-1 (x)

So

f -1 (-31/96)  =    ( 3 (-31/96)  + 1 )^(1/5)  = (3/96)^(1/5)  = .03125^(1/5)  = .5 =  1/2  !!!!!!