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3.3 · Q148

Q.Evaluate: ∫csc⁡(log⁡x)[1−cot⁡(log⁡x)]dx\int \csc(\log x)\left[1-\cot(\log x)\right]dx

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The stem as literally extracted, csc⁡(log⁡x)[1−cot⁡(log⁡x)]\csc(\log x)[1-\cot(\log x)], carries no explicit dx/xdx/x factor, and integrated purely 'dx' as printed this has no elementary closed form (it is not an e^x[f+f'] pattern like the rest of this group, since there is no e^x factor at all, and log x alone inside csc/cot with a bare dx does not reduce by any standard technique). This strongly suggests a 1x\dfrac1x factor was lost in extracting the source PDF (a known artifact in this source, since d(log⁡x)=dxxd(\log x)=\dfrac{dx}{x} is exactly what would make this integrable by substitution, matching the shape of the surrounding I.13/I.19/III.8 items which are all substitution-in-log-x problems). Solving under that assumption — i.e. treating the intended integral as ∫csc⁡(log⁡x)[1−cot⁡(log⁡x)]dxx\displaystyle\int\csc(\log x)\left[1-\cot(\log x)\right]\dfrac{dx}{x} — substitute t=log⁡xt=\log x, dt=dxxdt=\dfrac{dx}x:

∫csc⁡t(1−cot⁡t) dt=∫csc⁡t dt−∫csc⁡tcot⁡t dt\int\csc t(1-\cot t)\,dt=\int\csc t\,dt-\int\csc t\cot t\,dt …

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