Question Number 5495 by FilupSmith last updated on 16/May/16 $$\mathrm{Why}\:\mathrm{does}: \\ $$$$\mathrm{cos}^{\mathrm{2}} {x}=\frac{\mathrm{1}}{\mathrm{2}}\left(\mathrm{cos}\left(\mathrm{2}{x}\right)+\mathrm{1}\right) \\ $$ Commented by Yozzii last updated on 16/May/16 $${Let}\:\boldsymbol{{a}}=\begin{pmatrix}{{cosA}}\\{{sinA}}\end{pmatrix}\:,\boldsymbol{{b}}=\begin{pmatrix}{{cosB}}\\{−{sinB}}\end{pmatrix}. \\ $$$${For}\:{all}\:\mathrm{0}<{A},{B}<\mathrm{2}\pi,\:{the}\:{angle}\:{between}\:\boldsymbol{{a}}\:{and}\:\boldsymbol{{b}}\:{is}\:{A}+{B}…
Question Number 70997 by A8;15: last updated on 10/Oct/19 Answered by MJS last updated on 10/Oct/19 $$\mathrm{trying}\:\mathrm{first} \\ $$$$\mathrm{for}\:\mathrm{an}\:\mathrm{easy}\:\mathrm{solution}\:\mathrm{both}\:{a}+\mathrm{24}\:\mathrm{and}\:{a}+\mathrm{12} \\ $$$$\mathrm{must}\:\mathrm{be}\:\mathrm{square}\:\mathrm{numbers} \\ $$$$\Rightarrow\:{a}=−\mathrm{8}\:\Rightarrow\:{x}=−\mathrm{2} \\ $$…
Question Number 70969 by TawaTawa last updated on 10/Oct/19 Answered by mind is power last updated on 10/Oct/19 $${first}\:{find}\:{how}\:{many}\:{zero}\:{ends}\:\mathrm{80}! \\ $$$${n}=\left[\frac{\mathrm{80}}{\mathrm{5}}\right]+\left[\frac{\mathrm{80}}{\mathrm{25}}\right]=\mathrm{16}+\mathrm{3}=\mathrm{19} \\ $$$${so}\:{we}\:{have} \\ $$$$\mathrm{80}!={d}\ast\mathrm{10}^{\mathrm{19}}…
Question Number 136505 by rexford last updated on 22/Mar/21 Answered by Dwaipayan Shikari last updated on 22/Mar/21 $${Assuming}\:{soda}\:{was}\:{x}\:{litre}\:{in}\:{quantity} \\ $$$${Your}\:{consumption}=\frac{{x}}{\mathrm{2}}+\frac{{x}}{\mathrm{2}^{\mathrm{3}} }+\frac{{x}}{\mathrm{2}^{\mathrm{5}} }+…={x}\left(\frac{\mathrm{1}}{\mathrm{2}}+\frac{\mathrm{1}}{\mathrm{8}}+\frac{\mathrm{1}}{\mathrm{32}}+…\right) \\ $$$$=\frac{\frac{{x}}{\mathrm{2}}}{\mathrm{1}−\frac{\mathrm{1}}{\mathrm{4}}}=\frac{\mathrm{2}{x}}{\mathrm{3}} \\…
Question Number 136489 by liberty last updated on 22/Mar/21 $$\frac{\mathrm{1}}{\mathrm{2}}+\frac{\mathrm{2}}{\mathrm{4}}+\frac{\mathrm{3}}{\mathrm{8}}+\frac{\mathrm{6}}{\mathrm{16}}+\frac{\mathrm{11}}{\mathrm{32}}+\frac{\mathrm{20}}{\mathrm{64}}+\frac{\mathrm{37}}{\mathrm{128}}+…\:=? \\ $$ Answered by Olaf last updated on 22/Mar/21 $$\mathrm{Tribonacci}\:\mathrm{numbers}\:: \\ $$$$\mathrm{T}_{\mathrm{0}} \:=\:\mathrm{0},\:\mathrm{T}_{\mathrm{1}} \:=\:\mathrm{1},\:\mathrm{T}_{\mathrm{2}} \:=\:\mathrm{0}…
Question Number 136494 by liberty last updated on 22/Mar/21 $$\mathrm{5}\left(\sqrt{\mathrm{1}−{x}}\:+\sqrt{\mathrm{1}+{x}}\:\right)=\:\mathrm{6}{x}\:+\:\mathrm{8}\sqrt{\mathrm{1}−{x}^{\mathrm{2}} }\: \\ $$ Answered by MJS_new last updated on 22/Mar/21 $$\mathrm{I}\:\mathrm{get}\:\mathrm{2}\:\mathrm{solutions} \\ $$$${x}_{\mathrm{1}} =\frac{\mathrm{24}}{\mathrm{25}} \\…
Question Number 5414 by FilupSmith last updated on 14/May/16 $$\mathrm{How}\:\mathrm{do}\:\mathrm{we}\:\mathrm{prove}\:\mathrm{the}\:\mathrm{area}\:\mathrm{of}\:\mathrm{a}\:\mathrm{square}/\mathrm{rectangle} \\ $$$$\mathrm{is}\:\mathrm{at}\:\mathrm{its}\:\mathrm{maximum}\:\mathrm{when}\:\mathrm{both}\:\mathrm{sides}\:\mathrm{are}\:\mathrm{equal}. \\ $$$$ \\ $$$$\mathrm{So},\:\mathrm{if}\:\mathrm{we}\:\mathrm{have}\:\mathrm{a}\:\mathrm{rectangle}\:\mathrm{of}\:\mathrm{sides}\:{a}\:\mathrm{and}\:{b}, \\ $$$$\mathrm{how}\:\mathrm{do}\:\mathrm{we}\:\mathrm{show}\:\mathrm{its}\:\mathrm{maximized}\:\mathrm{when}\:{a}={b}? \\ $$ Answered by 123456 last updated…
Question Number 136475 by EDWIN88 last updated on 22/Mar/21 Commented by EDWIN88 last updated on 22/Mar/21 $$\mathrm{Use}\:\mathrm{the}\:\mathrm{fact}\:\mathrm{that}\:\mathrm{csc}\:\mathrm{x}\:=\:\frac{\mathrm{1}}{\mathrm{x}}+\frac{\mathrm{x}}{\mathrm{6}}+\frac{\mathrm{7x}^{\mathrm{3}} }{\mathrm{360}}+\frac{\mathrm{31x}^{\mathrm{5}} }{\mathrm{15120}}+…\:\mathrm{for}\:\mid\mathrm{x}\mid\:<\:\pi\:\mathrm{to} \\ $$$$\mathrm{find}\:\mathrm{the}\:\mathrm{first}\:\mathrm{four}\:\mathrm{terms}\:\mathrm{of}\:\mathrm{the}\:\mathrm{series}\:\mathrm{for} \\ $$$$\mathrm{2}\:\mathrm{csc}\:\left(\mathrm{2x}\right)\:\left[\:\mathrm{for}\:\mid\mathrm{x}\mid\:<\:\frac{\pi}{\mathrm{2}}\:\mathrm{and}\:\mathrm{thus}\:\mathrm{for}\:\mathrm{ln}\:\left(\mathrm{tan}\:\mathrm{x}\right).\right. \\ $$$$\left(\mathrm{a}\right)\:\mathrm{ln}\:\mid\mathrm{x}\mid\:+\frac{\mathrm{x}^{\mathrm{2}}…
Question Number 70920 by TawaTawa last updated on 09/Oct/19 $$\mathrm{i}\:!\:\:=\:\:? \\ $$ Commented by prakash jain last updated on 10/Oct/19 $${i}!=\Gamma\left(\mathrm{1}+{i}\right) \\ $$$$\mathrm{where}\:{i}=\sqrt{−\mathrm{1}} \\ $$…
Question Number 5386 by sanusihammed last updated on 12/May/16 $${Solve}\:{simultaneously} \\ $$$$ \\ $$$${x}^{{x}} \:+\:\:{y}^{{y}\:} \:=\:\:\mathrm{31} \\ $$$${x}\:\:+\:\:{y}\:\:=\:\:\mathrm{5} \\ $$$$ \\ $$$${Please}\:{i}\:{did}\:{workings}\:… \\ $$$$ \\…