## College Algebra (6th Edition)

x ... $\ \ y=0\ \$ ... horizontal
Book reference: Characteristics of Exponential Functions of the Form $f(x)=b^{x}$ (below Figure 4.4) 6. The graph of $f(x)=b^{x}$ (exponential function with base b) approaches, but does not touch,the [ x ] -axis . The x-axis, whose equation is [ $y=0$ ], is a [ horizontal ] asymptote.