Til the last breath-2

Calculus Level 4

T = 2 ϕ ( x 2 + x r = 1 x ( 0 1 ( 3 r 2 y 2 + 4 r y + r 2 ) d y ) ) d x {\mathfrak T=\int_{2}^{\color{forestgreen}{\phi}}\left(\dfrac{x^2+x}{\displaystyle\sum_{r=1}^{x}\left(\int_{0}^1\left( 3r^2y^2+4ry+r^2\right)\,dy\right)}\right)\,dx}

T = ln φ φ 8 \Large{\mathfrak{T}=\ln {\dfrac{\color{#EC7300}{\varphi^{\varphi}}}{8}}}

φ = ? \huge{ \color{#EC7300}{\varphi}=?}

Given

ϕ = ψ 4 + 1 \large\color{forestgreen}{\phi}=\dfrac{\color{#3D99F6}{\psi}}{4}+1

ψ = 8 216 8 216 \large\color{#3D99F6}{\psi}={\sqrt{8\sqrt{216\sqrt{8\sqrt{216\cdots}}}}}


Try the Part-1 here .


The answer is 3.

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1 solution

Rishabh Jain
Mar 18, 2016

0 1 ( 3 r 2 y 2 + 4 r y + r 2 ) d y = ( r 2 y 3 + 2 r 2 y 2 + r 2 y ) 0 1 = 2 ( r 2 + r ) \color{#302B94}{\begin{aligned} &\int_{0}^1\left( 3r^2y^2+4ry+r^2\right)\,dy\\&=(r^2y^3+2r^2y^2+r^2y)|_{0}^{1}\\& =2(r^2+r)\end{aligned}}


r = 1 x ( 0 1 ( 3 r 2 y 2 + 4 r y + r 2 ) d y ) = r = 1 x ( 2 r ( r + 1 ) ) = 2 ( r 2 + r ) \color{#302B94}{\displaystyle\sum_{r=1}^{x}\left(\int_{0}^1\left( 3r^2y^2+4ry+r^2\right)\,dy\right)\\ =\displaystyle\sum_{r=1}^{x}\left(2r(r+1)\right) \\=2(r^2+r)} Using formula for sum of n,n 2 ^2 expression can be simplified as: = 2 ( x ( x + 1 ) ( 2 x + 1 ) 6 + x ( x + 1 ) 2 ) = 2 x ( x + 1 ) ( x + 2 ) 3 \color{#302B94}{=2\left(\dfrac{x(x+1)(2x+1)}{6}+\dfrac{x(x+1)}{2}\right)~~~\\=\dfrac{2x(x+1)(x+2)}{3}}


T = 2 ϕ x ( x + 1 ) 2 x ( x + 1 ) ( x + 2 ) 3 d x \color{#302B94}{\mathfrak{T}=\int_{2}^{\color{forestgreen}{\phi}}\dfrac{\cancel{x(x+1)}}{\frac{2\cancel{x(x+1)}(x+2)}{3}}\, dx}\, = 3 2 ( ln ( ϕ + 2 4 ) ) \Large\color{#302B94}{=\dfrac 32(\ln(\color{forestgreen}{\dfrac{\phi+2}{4}}))}


ψ = 8 1 2 + 1 8 + 1 32 21 6 1 4 + 1 16 + 1 64 = 8 2 3 21 6 1 3 = 24 \Large\color{#3D99F6}{\psi}=\color{#624F41}{8^{\small{\frac 12+\frac18+\frac{1}{32}}}\cdot 216^{\small{\frac 14+\frac{1}{16}+\frac{1}{64}}}\\=8^{\small{\frac 23}}\cdot 216^{\small{\frac 13}}=24}

ϕ = ψ 4 + 1 = 7 \Large \color{forestgreen}{\phi}=\dfrac{\color{#3D99F6}{\psi}}{4}+1=\color{forestgreen}{7}


Hence, T = 3 2 ln 9 4 = ln 3 3 8 \Large \color{#EC7300}{\mathfrak T}=\color{#EC7300}{\dfrac 32\ln \dfrac 94=\ln \dfrac{3^3}{8}}

φ = 3 \Huge\therefore~\color{#0C6AC7}{ \varphi=}\color{#456461}{\boxed{\color{#EC7300}{\boxed{\color{#0C6AC7}{\mathbf{3}}}}}}

Great Problem!Keep posting such problems!

Anik Mandal - 5 years, 2 months ago

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Thanks... I'll be soon posting my 2700 2700 upvotes problem... Hope that you would like it too.. :-)

Rishabh Jain - 5 years, 2 months ago

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Yup looking forward to it..

Anik Mandal - 5 years, 2 months ago

Fantastic problem! Wonderful solution too :)

John Frank - 5 years, 2 months ago

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Thanks :-).......

Rishabh Jain - 5 years, 2 months ago

nicely framed question ,,

Rudraksh Sisodia - 4 years, 6 months ago

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