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Answer:
y = 0, also known as the x-axis.
Step-by-step explanation:
The equation [tex]f(x) = \frac{2}{3} ^{x}[/tex] is an exponential function.
There is an asymptote at y = 0, or the x-axis because:
[tex]\frac{2}{3} ^{x}\neq 0[/tex]
An exponential function, unless containing a vertical shift, can never cross the x-axis resulting in an asymptote at y = 0.