Let S be the set of all (α, β) ∈ R × R such that lim_(x → ∞) (sin(x²)(logₑ x)^α sin(1/x²))/(x^(αβ)(logₑ(1+x))^β) = 0 Then which of the following is (are) correct?
S⊆R2: limx→∞xαβ(ln(1+x))βsin(x2)(lnx)αsin(1/x2)=0
four given pairs (α,β)
Check: (−1,3), (−1,1), (1,−1), (1,−2) ∈S ?
sin(1/x2)∼x21,ln(1+x)∼lnx
∣sin(x2)∣≤1(bounded, oscillating)
xαβ(lnx)β(lnx)α⋅x21=x2+αβ(lnx)α−β
expression∼sin(x2)⋅x2+αβ(lnx)α−β
Since sin(x2) oscillates: limit =0⟺A(x)→0
A(x)=x2+αβ(lnx)α−β
2+αβ>0⇒A(x)→0
2+αβ<0⇒A(x)→∞
2+αβ=0⇒A(x)=(lnx)α−β→0⟺α<β
S={(α,β):αβ>−2}∪{(α,β):αβ=−2, α<β}
(1) (−1,3): αβ=−3<−2 ×
(2) (−1,1): αβ=−1>−2 ✓
(3) (1,−1): αβ=−1>−2 ✓
(4) (1,−2): αβ=−2, α>β ×
Correct options: (2) and (3)