8/28/2014 If f(x) = x² + 2x – 4 for x > 0, what is the value of f ^-1(4)?

a) 2

b) 4

c) 5

d) 8

e) 10

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8/28/2014 Solution. A. Since we need f ^-1(4), if f ^-1(4) = x, f(x) = 4 → x² + 2x – 4 = 4 so that x² + 2x – 8 = 0. Factoring and solving, x = 2.