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Ch. 7 - Transcendental Functions
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Non è quello che usi tu?Cambia libro di testo
Capitolo 7, Problema 7.1.63

Suppose that the range of g lies in the domain of f so that the composition fog is defined. If f and g are one-to-one, can anything be said about fog? Give reasons for your answer.

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Recall the definition of a one-to-one (injective) function: a function \( h \) is one-to-one if \( h(a) = h(b) \) implies \( a = b \).
Given that \( f \) and \( g \) are both one-to-one, consider the composition \( f \circ g \), defined by \( (f \circ g)(x) = f(g(x)) \).
To check if \( f \circ g \) is one-to-one, assume \( (f \circ g)(x_1) = (f \circ g)(x_2) \). This means \( f(g(x_1)) = f(g(x_2)) \).
Since \( f \) is one-to-one, \( f(g(x_1)) = f(g(x_2)) \) implies \( g(x_1) = g(x_2) \).
Because \( g \) is also one-to-one, \( g(x_1) = g(x_2) \) implies \( x_1 = x_2 \). Therefore, \( f \circ g \) is one-to-one.

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