Question Details

If β=limx0ex3(1x3)13+((1x2)121)sinxxsin2x, then the value of 6β is ___________ .

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Correct Answer :

5

Solution :

The correct answer is 5.

We are given the limit:
β=limx0ex3(1x3)13+((1x2)121)sinxxsin2x

Step 1: Simplify the denominator using standard limits
Recall that limx0sinxx=1.
Therefore, sin2x behaves like x2 as x0.
The denominator simplifies to:
xsin2x=x3(sinxx)2x3

Step 2: Expand the terms in the numerator up to order x3
Using Taylor series expansions around x=0:

1. Expansion of ex3:
ex3=1+x3+O(x6)

2. Expansion of (1x3)13 using the binomial expansion (1+y)n=1+ny+:
(1x3)13=113x3+O(x6)

3. Expansion of the third term ((1x2)121)sinx:
Using binomial expansion:
(1x2)12=112x2+O(x4)
So,
(1x2)121=12x2+O(x4)
Since sinx=xx36+O(x5), we have:
((1x2)121)sinx=(12x2+O(x4))(x+O(x3))=12x3+O(x5)

Step 3: Combine all terms in the numerator
Numerator =(1+x3)(113x3)+(12x3)+O(x4)
Numerator =1+x31+13x312x3+O(x4)
Numerator =(1+1312)x3+O(x4)
Numerator =(6+236)x3+O(x4)=56x3+O(x4)

Step 4: Evaluate the limit β
β=limx056x3+O(x4)x3=56

Step 5: Find the value of 6β
6β=6×56=5

Thus, the value of 6β is 5.

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