One-sided and two-sided limits of a simplifiable rational function
Consider the function . Note that is undefined at since both the numerator and denominator equal zero there.
The table below shows values of for near , approaching from both sides.
| 1.9 | 1.99 | 1.999 | 2 | 2.001 | 2.01 | 2.1 | |
|---|---|---|---|---|---|---|---|
| 2.9175 | 2.9917 | 2.9992 | undefined | 3.0008 | 3.0075 | 3.0758 |
Using this information (and/or algebraic simplification of ), find , , and , if each exists. State the value of itself, if it exists, and explain how it relates to the limit.
Hint
Factor the numerator as a difference of cubes and the denominator as a difference of squares, then cancel the common factor before evaluating the simplified expression at . Remember that the limit only depends on values of near 2, not on itself.
Step-by-step solution
Factor both numerator and denominator: and . For , the common factor cancels, giving . This simplified form agrees with everywhere except at , which is exactly what matters for evaluating limits since limits ignore the point itself.
Substituting into the simplified expression gives . Since this simplified function is continuous at , both the left-hand and right-hand limits equal 3, matching the table's trend (values approach 3 from both sides). Therefore , , and since these one-sided limits agree, . However, itself is undefined (0/0), illustrating that the limit exists even though the function has no value at that point.
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