Question Details

Let  be the set of all ( α , β ) R × R such that

lim x sin ( x 2 ) ( log e x ) α sin ( 1 x 2 ) x β ( log e ( 1 + x ) ) β = 0 .

Then which of the following is(are) correct ?

Options

A

( 1 , 3 ) S

B

( 1 , 1 ) S

C

( 1 , 1 ) S

D

( 1 , 2 ) S

Show Answer

Correct Answer :

Option C

( 1 , 1 ) S

Option B

( 1 , 1 ) S

Solution :

The correct options are ( - 1 , 1 ) (-1, 1) ∈ S and (1, -1) ∈ S.

Step 1: Simplify the asymptotic behavior of the functions as x → ∞
As x (i.e. x):
1. 1x20, so using the standard limit limt0sin(t)t=1, we have:

sin ( 1 x 2 ) 1 x 2

2. For the logarithmic term in the denominator:

log e ( 1 + x ) = log e ( x ( 1 + 1 x ) ) = log e x + log e ( 1 + 1 x ) log e x

Step 2: Rewrite the overall expression
Substituting these asymptotic approximations into the given limit expression:

lim x sin ( x 2 ) ( log e x ) α 1 x 2 x β ( log e x ) β = lim x sin ( x 2 ) x - ( 2 + β ) ( log e x ) α - β

Step 3: Analyze the convergence condition for the limit
Since sin(x2) is a bounded function oscillating continuously in the range [-1,1], the entire limit will evaluate to 0 if and only if the remaining algebraic factor decays to zero:

lim x x - ( 2 + β ) ( log e x ) α - β = 0

For polynomial-versus-logarithmic growth rates as x:
- If -(2+β)<0β>-2, the negative exponent of x places it in the denominator with a positive power. Since power functions grow strictly faster than any logarithmic power, the limit is 0 for any value of αR.

Step 4: Check the given options
1. For option (-1, 1): Here α=-1 and β=1. Since β=1>-2, it satisfies the condition. Hence, (-1,1) S.
2. For option (1, -1): Here α=1 and β=-1. Since β=-1>-2, it also satisfies the condition. Hence, (1,-1) S.

Unlock Our Free Library

Access expert-curated educational resources and study materials—completely free.

Discover more resources

You may also like

Mock Tests

View All
  • CTET
  • intermediate
  • No time limit
  • child development and pedagogy, mathematics, social science

  • SSC
  • intermediate
  • 2 hours and 30 mins
  • child development and pedagogy, mathematics, social science

Ask AI Tutor
5 left
Q1 View Question & Options
AI Tutor is solving this question...
Reading question context & options...