For , if then is equal to:
- A
- B
- C
- D
For , if then is equal to:
Correct answer:A
Standard Method
Given: for .
Find: .
Use Maclaurin expansions near .
As , the denominator tends to , so for the limit to be finite the numerator must also tend to :
Hence,
Now the numerator becomes
Using
we get
For the denominator,
and
So,
Since the numerator starts with the term of order , the coefficient of in the denominator must vanish for the limit to be finite and non-zero:
Then
Comparing coefficients of the lowest power term,
Thus,
Now,
Therefore, the correct option is A.
The solution concludes that , , and , so the required value is .
Coefficient Matching
Given: the limit equals .
Find: .
First set in the numerator condition for finiteness:
Then the numerator starts as
The denominator is
For the limit to be finite and non-zero, the -term must vanish:
Now compare the leading coefficients:
Hence,
Therefore, the correct option is A.
Setting only the denominator to zero and forgetting that the numerator must also approach for a finite limit. This misses the condition . First enforce finiteness, then compare series terms.
Keeping the linear term in the denominator. Since the numerator begins with , a nonzero linear term would make the limit either or undefined, not a finite non-zero constant. Therefore is necessary.
Using the wrong coefficient in . The correct expansion is . An incorrect cubic coefficient gives a wrong value of .
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