Evaluating a function

If f(x) = x^(-2/3), what is the value of f(8) ?

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f(x) = x^(-2/3)

1
--------- = f(x) {made a positive exponent by moving into denominator}
x^(2/3)

1
--------- = f(8) {substituted 8 for x}
8^(2/3)

1
---------- = f(8) {8 to the two-thirds power is the same as the cube root of 8, squared}
(³√8)²

1
------ = f(8) {evaluated the cube root of 8 to be 2}
2²

1
--- = f(8) {squared the 2}
4

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