Let A be a nonempty set and let f : A→ A be a function. Prove that if f o f = i4, then f is bijective.

Are the signs of the coefficients on the variables "Frequency of Flights" and "Destination is a Big City" corresponding to the utility of the "Air" mode meaningful?   Utility for Car Utility for Air   param.  t stat Param. t stat Constant 4.77 6.995 0 fixed Travel Time (mins) -0.03 -16.926 -0.03 -16.926 Travel Cost / Income ($/$) -726.35 -4.28 -726.35 -4.28 Frequency of Flights (per week) 0 fixed 0.12 13.414 Is Destination a Large City 0 fixed 1.5 5.576 Travel Party Size > =2^2 1.75 5.873 0 Fixed

3.7.1 only

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Use linear approximation to estimate the value of 28 /28 5.15 5.2 5.25 5.3