A calculus problem by Rohan Shinde

Calculus Level 5

If 0 sin ( x 2 ) ln 2 x d x = 1 4 π R ( π + O 1 ψ ( H ) ( 1 A ) ) N \int_0^{\infty} \sin (x^2) \ln^2 x\ dx= \frac 14 \sqrt {\frac {\pi}{R}}\left(\pi +O_1 \psi^{(H)}\left(\frac 1A \right)\right)^N

is true for non-negative integers R , O 1 , H , A , N R, O_1,H,A,N then find R + O 1 + H + A + N R+O_1+H+A+N

Note: ψ ( m ) ( z ) \psi^{(m)} (z) is the Polygamma function i.e ( m + 1 ) t h (m+1)^{th} derivative of ln ( Γ ( z ) ) \ln(\Gamma(z))


The answer is 134.

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1 solution

Rohan Shinde
Jan 22, 2019

I = 0 sin ( x 2 ) ln 2 x d x I=\int_0^{\infty} \sin (x^2) \ln^2xdx

Substituting x 2 = t x^2=t

I = 1 8 0 t 1 2 sin t ln 2 t d t I=\frac 18\int_0^{\infty} t^{-\frac 12} \sin t \ln^2tdt

Define J ( a ) = 1 8 0 t a 1 sin t d t = 1 8 0 t a ( k = 0 ( 1 ) k t 2 k Γ ( k + 1 ) k ! Γ ( 2 + 2 k ) ) d t J(a)=\frac 18 \int_0^{\infty} t^{a-1}\sin t dt=\frac 18\int_0^{\infty} t^a \left(\sum_{k=0}^{\infty} \frac {(-1)^k t^{2k}\Gamma(k+1)}{k!\Gamma(2+2k)}\right)dt

Using Ramanujan's Master theorem this evaluates to J ( a ) = 1 16 Γ ( s ) ϕ ( s ) J(a)=\frac {1}{16}\Gamma(s)\phi(-s) where s = a + 1 2 s=\frac {a+1}{2} and ϕ ( k ) = Γ ( k + 1 ) Γ ( 2 + 2 k ) \phi(k)=\frac {\Gamma(k+1)}{\Gamma(2+2k)}

What we need to find I I is just J ( 1 / 2 ) J''(1/2) which from above formulation would yield the answer as 1 4 π 128 ( π + 2 ψ ( 0 ) ( 1 2 ) ) 2 \frac 14\sqrt {\frac {\pi}{128}}\left(\pi+2\psi^{(0)}\left(\frac 12\right)\right)^2

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