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Calculus Level 4

lim n ( 1 2016 + 2 2016 + + n 2016 n 2017 ) = ψ lim n ( 1 2017 + 2 2017 + + n 2017 n 2018 ) \lim_{n\rightarrow\infty}\left(\dfrac{1^{2016}+2^{2016}+\cdots+n^{2016}}{n^{2017}}\right)=\color{#EC7300}{\psi}\lim_{n\rightarrow\infty}\left(\dfrac{1^{2017}+2^{2017}+\cdots+n^{2017}}{n^{2018}}\right) If above equation holds true we get ψ = 1 + 1 β \color{#EC7300}{\psi}=1+\dfrac{1}{\color{#302B94}{\beta}} such that 2 ( β 1 ) = ϕ ( ϕ + 1 ) 2(\color{#302B94}{\beta}-1)=\color{forestgreen}{\phi}(\color{forestgreen}{\phi}+1) .

P = n = ϕ + 1 3 ϕ ( 1 n 2 + 3 n + 2 ) \Large\mathfrak{P}=\sum_{n=\sqrt[3]{\color{forestgreen}{\phi+1}}}^{\color{forestgreen}{\phi}}\left(\dfrac{1}{n^2+3n+2}\right) If P \mathfrak{P} can be represented in the form δ α \color{#D61F06}{\dfrac{\delta}{\alpha}} , then find α δ + 1 \color{#D61F06}{\dfrac{\alpha}{\delta+1}} .


Details: \textbf{Details:}

ψ R ; β , ϕ , α , δ Z \psi\in\mathbb R ~~;\beta,\phi,\alpha,\delta \in\mathbb{Z} .

δ \delta and α \alpha are coprime.


The answer is 5.

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1 solution

Rishabh Jain
Mar 11, 2016

ψ = lim n ( 1 2016 + 2 2016 + + n 2016 n 2017 ) lim n ( 1 2017 + 2 2017 + + n 2017 n 2018 ) \large\color{#EC7300}{\psi}=\dfrac{\displaystyle\lim_{n\rightarrow\infty}\left(\dfrac{1^{2016}+2^{2016}+\cdots+n^{2016}}{n^{2017}}\right)}{\displaystyle\lim_{n\rightarrow\infty}\left(\dfrac{1^{2017}+2^{2017}+\cdots+n^{2017}}{n^{2018}}\right)} = lim n 1 n r = 1 n ( r n ) 2016 lim n 1 n r = 1 n ( r n ) 2017 \large =\dfrac{\displaystyle\lim_{n\rightarrow\infty}\dfrac 1n \displaystyle\sum_{r=1}^{n}\left(\dfrac rn\right)^{2016}}{\displaystyle\lim_{n\rightarrow\infty}\dfrac 1n \displaystyle\sum_{r=1}^{n}\left(\dfrac rn\right)^{2017}} Using Riemann Sums = 0 1 x 2016 0 1 x 2017 \Large =\dfrac{\int_0^1 x^{2016}}{\int_0^1 x^{2017}} = 2018 2017 = 1 + 1 2017 \large =\dfrac{2018}{2017}=1+\dfrac{1}{2017} β = 2017 \large\color{#302B94}{\beta=2017} 2 ( 2017 1 ) = 63 ( 64 ) ϕ = 63 2(2017-1)=63(64)\implies \color{forestgreen}{\phi=63} P = n = 4 63 ( 1 n + 1 1 n + 2 ) \Large\mathfrak{P}=\sum_{n=\color{forestgreen}{4}}^{\color{forestgreen}{63}}\left(\dfrac{1}{n+1}-\dfrac{1}{n+2}\right) (A Telescopic Series) \large\color{#69047E}{\textbf{(A Telescopic Series)}} = 1 5 1 65 = 12 65 = δ α \large=\dfrac 15-\dfrac{1}{65}=\dfrac{12}{65}=\color{#D61F06}{\dfrac{\delta}{\alpha}} 65 13 = 5 \therefore \Huge \dfrac{65}{13}= \Huge\color{#456461}{\boxed{\color{#D61F06}{\boxed{\Huge\color{#007fff}{5}}}}}

For someone not knowing Reimann Sums , one can proove by induction 😛

Aakash Khandelwal - 5 years, 3 months ago

I just loved the way the problem unfolded encompassing two of pivotal concepts! (+1)

Pulkit Gupta - 5 years, 3 months ago

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Ya.... It took a bit of time to design the problem but I'm glad you loved the problem. Go try this too.. ;-p - which is a blend of few concepts of Reimann sums and Properties of Integrations.. You'll surely love it..

Rishabh Jain - 5 years, 3 months ago

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