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Estimating a limit numerically near a hole in the domain

Consider the function g(x)=x−3x−9g(x) = \dfrac{\sqrt{x} - 3}{x - 9}. Note that g(x)g(x) is not defined at x=9x = 9, since this gives 00\frac{0}{0}. We want to understand how g(x)g(x) behaves for values of xx near 9, even though it is undefined at 9.

Use a calculator or spreadsheet to evaluate g(x)=x−3x−9g(x) = \dfrac{\sqrt{x} - 3}{x - 9} at values of xx close to 99 on both sides, such as x=8.9,8.99,8.999x = 8.9, 8.99, 8.999 and x=9.1,9.01,9.001x = 9.1, 9.01, 9.001. Organize your results in a table (you do not need to submit the table itself). Based on the trend you observe as xx gets closer and closer to 99 from both sides, what is lim⁡x→9g(x)\displaystyle\lim_{x \to 9} g(x)?

Estimating a limit numerically near a hole in the domain graph
Hint

Notice that g(x)g(x) is undefined at x=9x=9 itself, but you are asked about its behavior for xx values approaching 9, not at 9. Watch what value the outputs seem to settle toward as xx gets closer to 9 from each side.

Step-by-step solution

As xx approaches 99 from the left (e.g., x=8.9,8.99,8.999x = 8.9, 8.99, 8.999), computing g(x)=x−3x−9g(x) = \frac{\sqrt{x}-3}{x-9} gives values that get closer and closer to 0.16‾0.1\overline{6}, i.e. approximately 0.16670.1667. Similarly, approaching from the right (e.g., x=9.1,9.01,9.001x = 9.1, 9.01, 9.001) also produces values approaching about 0.16670.1667. Since the function is undefined exactly at x=9x=9, we rely entirely on this trend from nearby values rather than trying to plug in x=9x=9 directly.

Because both the left-hand and right-hand trends converge to the same numerical value, approximately 0.16670.1667, we conclude that the two-sided limit exists and equals this common value. This matches the algebraic value 1/61/6 (obtainable by rationalizing x−3\sqrt{x}-3, though that technique isn't required here), confirming lim⁡x→9g(x)≈1/6\lim_{x\to 9} g(x) \approx 1/6.

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