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1-n-n-n-1-2-n-n-1-n-2-3-n-n-1-n-2-n-3-4-

Question Number 37728 by kunal1234523 last updated on 17/Jun/18 $$\mathrm{1}+\mathrm{n}+\frac{\mathrm{n}\left(\mathrm{n}−\mathrm{1}\right)}{\mathrm{2}!}+\frac{\mathrm{n}\left(\mathrm{n}−\mathrm{1}\right)\left(\mathrm{n}−\mathrm{2}\right)}{\mathrm{3}!}+\frac{\mathrm{n}\left(\mathrm{n}−\mathrm{1}\right)\left(\mathrm{n}−\mathrm{2}\right)\left(\mathrm{n}−\mathrm{3}\right)}{\mathrm{4}!}+……..= \\ $$ Answered by tanmay.chaudhury50@gmail.com last updated on 17/Jun/18 $$\left(\mathrm{1}+{x}\right)^{{n}} =\mathrm{1}+{nC}_{\mathrm{1}} {x}+{nC}_{\mathrm{2}} {x}^{\mathrm{2}} +{nC}_{\mathrm{3}} {x}^{\mathrm{3}}…

A-commitee-of-2-boys-and-1-girl-has-to-be-formed-from-a-class-of-4-boys-and-3-girls-give-the-number-of-ways-these-can-be-done-

Question Number 37711 by Rio Mike last updated on 16/Jun/18 $${A}\:{commitee}\:{of}\:\mathrm{2}\:{boys}\:{and}\:\mathrm{1}\:{girl} \\ $$$${has}\:{to}\:{be}\:{formed}\:{from}\:{a}\:{class} \\ $$$${of}\:\mathrm{4}\:{boys}\:{and}\:\mathrm{3}\:{girls}\:{give}\:{the}\:{number} \\ $$$${of}\:{ways}\:{these}\:{can}\:{be}\:{done} \\ $$ Answered by math1967 last updated on…

2-6-12-20-30-42-n-1-3-n-n-1-n-2-is-this-true-if-yes-so-please-derive-it-from-L-H-S-hey-I-just-noticed-I-got-15yrs-and-5-months-older-

Question Number 37692 by kunal1234523 last updated on 16/Jun/18 $$\mathrm{2}+\mathrm{6}+\mathrm{12}+\mathrm{20}+\mathrm{30}+\mathrm{42}+………+\mathrm{n}=\frac{\mathrm{1}}{\mathrm{3}}\left(\mathrm{n}\right)\left(\mathrm{n}−\mathrm{1}\right)\left(\mathrm{n}−\mathrm{2}\right) \\ $$$$\mathrm{is}\:\mathrm{this}\:\mathrm{true}.\:\mathrm{if}\:\mathrm{yes}\:\mathrm{so}\:\mathrm{please}\:\mathrm{derive}\:\mathrm{it}\:\mathrm{from}\:\mathrm{L}.\mathrm{H}.\mathrm{S} \\ $$$$\mathrm{hey}\:\mathrm{I}\:\mathrm{just}\:\mathrm{noticed}\:\mathrm{I}\:\mathrm{got}\:\mathrm{15yrs}\:\mathrm{and}\:\:\mathrm{5}\:\mathrm{months}\:\mathrm{older} \\ $$ Answered by tanmay.chaudhury50@gmail.com last updated on 16/Jun/18 $${s}=\mathrm{2}+\mathrm{6}+\mathrm{12}+\mathrm{20}+\mathrm{30}+\mathrm{42}+…+{T}_{{n}−\mathrm{1}} +{T}_{{n}}…

1-1-1-1-1-1-1-S-n-S-n-1-1-1-1-1-1-1-2S-n-2-2-2-subtracting-S-n-1-1-1-1-1-1-1-1-1-1-S-n-1-2-S-n-1-2-I-have-found-this-while-experim

Question Number 103219 by Dwaipayan Shikari last updated on 13/Jul/20 $$\mathrm{1}+\mathrm{1}+\mathrm{1}+\mathrm{1}+\mathrm{1}+\mathrm{1}+\mathrm{1}+….={S}_{{n}} \\ $$$${S}_{{n}} =\mathrm{1}+\mathrm{1}+\mathrm{1}+\mathrm{1}+\mathrm{1}+\mathrm{1}+\mathrm{1}+…. \\ $$$$\mathrm{2}{S}_{{n}} =\:\:\:\:\mathrm{2}\:+\:\:\:\:\:\:\mathrm{2}\:\:\:+\:\:\:\:\:\mathrm{2}+……. \\ $$$$……….\:{subtracting} \\ $$$$−{S}_{{n}} =\mathrm{1}−\mathrm{1}+\mathrm{1}−\mathrm{1}+\mathrm{1}−\mathrm{1}+\mathrm{1}−\mathrm{1}+\mathrm{1}−\mathrm{1}+…. \\ $$$$−{S}_{{n}} =\frac{\mathrm{1}}{\mathrm{2}}…