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put this solution on YOUR website!y = 8(2x^3 - 9)^7
x = 8(2y^3 - 9)^7
x/8 = (2y^3 - 9)^7
(x/8)^(1/7) = 2y^3 - 9
(x/8)^(1/7) + 9 = 2y^3
(x/8)^(1/7)/2 + 9/2 = y^3
((x/8)^(1/7)/2 + 9/2)^(1/3) = y
f(x) = 8(2x^3 - 9)^7
f^-1(x) = ((x/8)^(1/7)/2 + 9/2)^(1/3)