γ n = H n − lo g n , n ≥ 1 , x ∈ R Find Ω ( x ) = n → ∞ lim ( n 1 i = 1 ∑ n γ i sin 2 x ⋅ γ n + 1 − i cos 2 x )
Find the value lo g 1 0 ( Ω ( x ) ) .
This is the proposal of Professor Daniel Sitaru and the problem original source is Romanian Mathematical Mazagine .
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You're mixing the notation for logarithms - sometimes " lo g " means "natural logarithm" and sometimes it doesn't.
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This is a very nice analysis problem as it's been also solved by Sir Ali Jaffal from Lebanon in complete analysis way.
Here is my try for solution
For convenience we write sin 2 x = S ( x ) and cos 2 x = C ( x ) then we observe that ψ ( n ) = i = 1 ∑ n γ i S ( x ) ⋅ γ n + 1 − i C ( x ) = i = 1 ∑ n k = n + 1 − i ∑ n γ i S ( x ) γ k C ( x ) = i = 1 ∑ n γ i S ( x ) k = 1 ∑ n γ k C ( x ) = m = 1 ∑ n γ m S ( x ) + C ( x ) = m = 1 ∑ n γ m ( for i = k = m ) since S ( x ) + C ( x ) = 1 Now n → ∞ lim n ψ ( n ) = n → ∞ lim n 1 m = 1 ∑ n γ m = n → ∞ lim n 1 m = 1 ∑ n ( H m − lo g m ) = n → ∞ lim n 1 ( m = 1 ∑ n j = 1 ∑ m j 1 − lo g ( m = 1 ∏ n m ) ) = n → ∞ lim n 1 ( m = 1 ∑ n m n − m + 1 − lo g ( n ! ) ) = n → ∞ lim ( m = 1 ∑ n m 1 − n n lo g n − n + O lo g ( n ) − 1 + n 1 m = 1 ∑ n n 1 ) ∴ Ω ( x ) = n → ∞ lim ( m = 1 ∑ n m 1 − lo g n ) + 0 = γ and hence lo g ( Ω ( x ) ) = lo g ( γ ) = − 0 . 2 3 8 6 6 1 ⋯ .