The shaded area is equal to . It is also equal to , for some positive number . Find .
Notation: is the modified Bessel function of the second kind . (You don't have to worry about it in this question) .
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ln ( x y ) = ( ln x ) ( ln y )
Converting to polar form
⟹ r = sin θ cos θ exp ( 1 − 2 1 ln 2 tan θ + 4 )
Required area = A = 2 1 ∫ 0 2 π r 2 d θ
= ∫ 0 4 π csc θ sec θ exp ( 2 − ln 2 tan θ + 4 ) d θ
Let ln tan θ = t ⟹ d t = csc θ sec θ d θ
⟹ A = ∫ − ∞ 0 e 2 − t 2 + 4 d t = ∫ 0 ∞ e 2 − t 2 + 4 d t
By Inverting the function, the integral becomes:
∫ 0 1 ln 2 x − 4 ln x d x
⟹ α = 4