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An exponential function $f(x)=b^x$ is always positive.

The function $f(x)=ab^x$ has a horizontal asymptote at $y=0\text{.}$

The value of $b$ determines how rapidly the graph of $f(x)=ab^x$ increases or decreases.

The graph of $f(x)=ab^x$ is decreasing if $b \lt 0\text{.}$