Let be a positive integer.
(1): Let and
and have common tangents at points and .
Let be the area of the region bounded by and the line and .
(2): Let and .
and have common tangents at points and .
Let be the area of the region bounded by and the line and .
Find: . .
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
Let f ( x ) = x 2 n + 1 and g ( x ) = lo g b ( x ) = ln ( b ) ln ( x ) for x > 0
⟹ f ′ ( a ) = ( 2 n + 1 ) a 2 n = g ′ ( a ) = a ln ( b ) 1 ⟹ a 2 n + 1 = ( 2 n + 1 ) ln ( b ) 1 ⟹ a = ( ( 2 n + 1 ) ln ( b ) 1 ) 2 n + 1 1
and
a 2 n + 1 = ln ( b ) ln ( a ) ⟹ ( 2 n + 1 ) ln ( b ) 1 = ( 2 n + 1 ) ln ( b ) ln ( ( 2 n + 1 ) ln ( b ) 1 ) ⟹ ln ( ( 2 n + 1 ) ln ( b ) 1 ) = 1 ⟹ ln ( b ) = 2 n + 1 ) e 1 ⟹
b = e ( 2 n + 1 ) e 1 ⟹ a = e 2 n + 1 1 ⟹ a 2 n + 1 = e
⟹ A : ( e 2 n + 1 1 , e ) and using the symmetry about the origin we have A ′ : ( − e 2 n + 1 1 , − e )
⟹ m A A ′ = e 2 n + 1 2 n ⟹ y = e 2 n + 1 2 n x
⟹ A n = 2 ∫ 0 e 2 n + 1 1 ( e 2 n + 1 2 n x − x 2 n + 1 ) d x = ( n + 1 n ) e 2 n + 1 2 n + 2
⟹ L = lim n → ∞ A n = e lim n → ∞ ( 1 − n + 1 1 ) e 2 n + 1 1 = e .
Using the symmetry about the y axis we have:
f ( x ) = x 2 n and g ( x ) = lo g b ( x ) = ln ( b ) ln ( x ) ⟹ f ′ ( a ) = 2 n a 2 n − 1 = g ′ ( a ) = a ln ( b ) 1 ⟹ a 2 n = 2 n ln ( b ) 1 ⟹ a = ( 2 n ln ( b ) 1 ) 2 n 1
and
a 2 n = ln ( b ) ln ( a ) ⟹ 2 n ln ( b ) 1 = 2 n ln ( b ) ln ( 2 n ln ( b ) 1 )
⟹ 1 = ln ( 2 n ln ( b ) 1 ) ⟹ 2 n ln ( b ) = e 1 ⟹ ln ( b ) = 2 n e 1 ⟹ b = e 2 n e 1 ⟹ a = e 2 n 1 and a 2 n = e .
⟹ B ( e 2 n 1 , e ) and using the symmetry about the y axis we have
B ′ ( − e 2 n 1 , e ) and line B B ′ is y = e ⟹ A n ∗ = 2 ∫ 0 e 2 n 1 ( e − x 2 n ) d x = 2 ( 2 n + 1 2 n ) e 2 n 2 n + 1
⟹ L ∗ = lim n → ∞ A n ∗ = 2 e lim n → ∞ ( 1 − 2 n + 1 1 ) e 2 n 1 = 2 e
∴ L L ∗ = 2 .