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Author: Tinku Tara

Question-7514

Question Number 7514 by Tawakalitu. last updated on 01/Sep/16 Answered by Yozzia last updated on 01/Sep/16 $${sin}\left(\pi{cos}\alpha\right)={cos}\left(\pi{sin}\alpha\right). \\ $$$${Using}\:{sina}={cos}\left(\frac{\pi}{\mathrm{2}}−{a}\right),\:{we}\:{get} \\ $$$${cos}\left(\frac{\pi}{\mathrm{2}}−\pi{cos}\alpha\right)={cos}\left(\pi{sin}\alpha\right) \\ $$$$\Rightarrow\frac{\pi}{\mathrm{2}}−\pi{cos}\alpha=\mathrm{2}{n}\pi\pm\pi{sin}\alpha\:\:\:\:\left({n}\in\mathbb{Z}\right) \\ $$$$\mp\pi{sin}\alpha−\pi{cos}\alpha=\mathrm{2}{n}\pi−\frac{\pi}{\mathrm{2}}…

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Question Number 73044 by mathmax by abdo last updated on 05/Nov/19 $${prove}\:{that}\:\:\sum_{{k}=\mathrm{1}} ^{{n}} \:{H}_{{k}} =\left({n}+\mathrm{1}\right){H}_{{n}} −{n} \\ $$$${and}\:\sum_{{k}=\mathrm{1}} ^{{n}} \:{H}_{{k}} ^{\mathrm{2}} \:=\left({n}+\mathrm{1}\right){H}_{{n}} ^{\mathrm{2}} \:−\left(\mathrm{2}{n}+\mathrm{1}\right){H}_{{n}} \:+\mathrm{2}{n}…

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Question Number 73042 by mathmax by abdo last updated on 05/Nov/19 $${prove}\:{that}\:{for}\:\left({n},{p}\right)\in{N}^{\bigstar^{\mathrm{2}} } \:\:\:\sum_{{k}=\mathrm{0}} ^{{p}\:} \:{k}\:{C}_{{n}} ^{{p}−{k}} \:{C}_{{n}} ^{{k}} \:={n}\:{C}_{\mathrm{2}{n}−\mathrm{1}} ^{{p}−\mathrm{1}} \\ $$$${conclude}\:{the}\:{value}\:{of}\:\sum_{{k}=\mathrm{0}} ^{{n}} \:{k}\:\left({C}_{{n}}…