Question Number 190340 by ajfour last updated on 01/Apr/23
Commented by a.lgnaoui last updated on 01/Apr/23
Commented by a.lgnaoui last updated on 01/Apr/23
Commented by mr W last updated on 01/Apr/23
Commented by mr W last updated on 01/Apr/23
$${there}\:{are}\:{infinite}\:{equilateral}\:{triangles}. \\ $$$${one}\:{is}\:{the}\:{smallest}\:\left({red}\:{one}\right)\:{and}\:{one} \\ $$$${is}\:{the}\:{largest}\:\left({green}\:{one}\right). \\ $$
Answered by a.lgnaoui last updated on 01/Apr/23
$${soit}\:{MN}\:{Droites}\:{tengent}\:{aux}\:{cercles} \\ $$$${MN}\mid\mid\:{EA}\:\:{et}\:\:{EA}\mid\mid{BC} \\ $$$${C}_{\mathrm{1}} \left({O}_{\mathrm{1}} ,{b}\right)\:\:{et}\:{cercleC}_{\mathrm{2}} \left({O}_{\mathrm{2}} ,{a}\right) \\ $$$${triangle}\:{EAO}_{\mathrm{2}} \left({Equilaterale}\right) \\ $$$${OA}={R} \\ $$$${point}\:{A}\:{tel}\:{que}\:{O}_{\mathrm{2}} {A}={EA}={R} \\ $$$${R}={a}+{b} \\ $$$$\mathrm{tan}\:\frac{\pi}{\mathrm{6}}=\frac{{R}}{\mathrm{2}{h}}=\frac{\sqrt{\mathrm{3}}}{\mathrm{3}}\Rightarrow{h}=\frac{\left({a}+{b}\right)\sqrt{\mathrm{3}}}{\mathrm{2}} \\ $$$$\bigtriangleup{ABC}\:\:\:{AEO}_{\mathrm{2}} \:\:{semblables} \\ $$$$\:\frac{{h}}{{S}+{a}}=\frac{\sqrt{\mathrm{3}}}{\mathrm{2}}\Rightarrow{S}=\frac{\mathrm{2}{h}}{\:\sqrt{\mathrm{3}}}−{a} \\ $$$${S}=\left({a}+{b}\right)−{a} \\ $$$$\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\boldsymbol{{S}}=\boldsymbol{{b}} \\ $$
Answered by ajfour last updated on 01/Apr/23
Commented by ajfour last updated on 07/Apr/23
$${B}\left(\mathrm{0},{b}\right)\:\:\:{A}\left(\mathrm{0},−{a}\right) \\ $$$${Q}\left({b}\mathrm{sin}\:\phi,\:{b}−{b}\mathrm{cos}\:\phi\right) \\ $$$${P}\left({a}\mathrm{sin}\:\theta,−{a}+{a}\mathrm{cos}\:\theta\right) \\ $$$${let}\:\:{M}\left({h},{k}\right) \\ $$$${b}\mathrm{sin}\:\phi={h}+\frac{{s}}{\mathrm{2}}\mathrm{cos}\:\delta \\ $$$${b}−{b}\mathrm{cos}\:\phi={k}+\frac{{s}}{\mathrm{2}}\mathrm{sin}\:\delta \\ $$$${a}\mathrm{sin}\:\theta={h}−\frac{{s}}{\mathrm{2}}\mathrm{cos}\:\delta \\ $$$$−{a}+{a}\mathrm{cos}\:\theta={k}−\frac{{s}}{\mathrm{2}}\mathrm{sin}\:\delta \\ $$$$\Rightarrow\:\:\mathrm{2}{k}={b}−{a}+{a}\mathrm{cos}\:\theta−{b}\mathrm{cos}\:\phi \\ $$$${s}\mathrm{sin}\:\delta={b}+{a}−{a}\mathrm{cos}\:\theta−{b}\mathrm{cos}\:\phi \\ $$$$\mathrm{2}{h}={b}\mathrm{sin}\:\phi+{a}\mathrm{sin}\:\theta \\ $$$${s}\mathrm{cos}\:\delta={b}\mathrm{sin}\:\phi−{a}\mathrm{sin}\:\theta \\ $$$${T}\left({p},{q}\right) \\ $$$${p}={h}+\frac{{s}\sqrt{\mathrm{3}}}{\mathrm{2}}\mathrm{sin}\:\delta \\ $$$${q}={k}−\frac{{s}\sqrt{\mathrm{3}}}{\mathrm{2}}\mathrm{cos}\:\delta \\ $$$$\left({h}+\frac{{s}\sqrt{\mathrm{3}}}{\mathrm{2}}\mathrm{sin}\:\delta\right)^{\mathrm{2}} +\left({k}−\frac{{s}\sqrt{\mathrm{3}}}{\mathrm{2}}\mathrm{cos}\:\delta−{b}+{a}\right)^{\mathrm{2}} \\ $$$$=\left({a}+{b}\right)^{\mathrm{2}} \\ $$$$\theta\:{and}\:\phi\:\:{are}\:{then}\:{related}\:{herein} \\ $$$$\left\{{b}\mathrm{sin}\:\phi+{a}\mathrm{sin}\:\theta+\sqrt{\mathrm{3}}\left({b}+{a}−{a}\mathrm{cos}\:\theta−{b}\mathrm{cos}\:\phi\right)\right\}^{\mathrm{2}} \\ $$$$+\left\{\left({b}−{a}+{a}\mathrm{cos}\:\theta−{b}\mathrm{cos}\:\phi\right)\right. \\ $$$$\left.\:\:\:\:\:\:\:\:−\sqrt{\mathrm{3}}\left({b}\mathrm{sin}\:\phi−{a}\mathrm{sin}\:\theta\right)−\mathrm{2}\left({b}−{a}\right)\right\}^{\mathrm{2}} \\ $$$$=\mathrm{4}\left({a}+{b}\right)^{\mathrm{2}} \\ $$$${while} \\ $$$${s}^{\mathrm{2}} =\left({b}+{a}−{a}\mathrm{cos}\:\theta−{b}\mathrm{cos}\:\phi\right)^{\mathrm{2}} \\ $$$$\:\:\:\:\:\:\:\:+\left({b}\mathrm{sin}\:\phi−{a}\mathrm{sin}\:\theta\right)^{\mathrm{2}} \\ $$$$….. \\ $$
Answered by mr W last updated on 02/Apr/23
Commented by mr W last updated on 04/Apr/23
$${r}={a}+{b} \\ $$$${C}\left({r}\:\mathrm{sin}\:\theta,\:{r}\:\mathrm{cos}\:\theta\right) \\ $$$$\left({x}−{r}\:\mathrm{sin}\:\theta\right)^{\mathrm{2}} +\left({y}−{r}\:\mathrm{cos}\:\theta\right)^{\mathrm{2}} ={s}^{\mathrm{2}} \\ $$$${point}\:{A}: \\ $$$$\left({x}_{{A}} −{r}\:\mathrm{sin}\:\theta\right)^{\mathrm{2}} +\left({y}_{{A}} −{r}\:\mathrm{cos}\:\theta\right)^{\mathrm{2}} ={s}^{\mathrm{2}} \\ $$$$\left({x}_{{A}} −{b}\right)^{\mathrm{2}} +{y}_{{A}} ^{\mathrm{2}} ={a}^{\mathrm{2}} \\ $$$$\left({b}−{r}\:\mathrm{sin}\:\theta\right)\left(\mathrm{2}{x}_{{A}} −{b}−{r}\:\mathrm{sin}\:\theta\right)−{r}\:\mathrm{cos}\:\theta\:\left(\mathrm{2}{y}_{{A}} −{r}\:\mathrm{cos}\:\theta\right)={s}^{\mathrm{2}} −{a}^{\mathrm{2}} \\ $$$$\mathrm{2}\left({b}−{r}\:\mathrm{sin}\:\theta\right){x}_{{A}} −\mathrm{2}{r}\:\mathrm{cos}\:\theta\:{y}_{{A}} ={s}^{\mathrm{2}} −{a}^{\mathrm{2}} +{b}^{\mathrm{2}} −{r}^{\mathrm{2}} ? \\ $$$$\Rightarrow{y}_{{A}} =\frac{\mathrm{2}\left({b}−{r}\:\mathrm{sin}\:\theta\right){x}_{{A}} −{s}^{\mathrm{2}} +{a}^{\mathrm{2}} −{b}^{\mathrm{2}} +{r}^{\mathrm{2}} }{\mathrm{2}{r}\:\mathrm{cos}\:\theta} \\ $$$$\left({x}_{{A}} −{b}\right)^{\mathrm{2}} +\left[\frac{\mathrm{2}\left({b}−{r}\:\mathrm{sin}\:\theta\right){x}_{{A}} −{s}^{\mathrm{2}} +{a}^{\mathrm{2}} −{b}^{\mathrm{2}} +{r}^{\mathrm{2}} }{\mathrm{2}{r}\:\mathrm{cos}\:\theta}\right]^{\mathrm{2}} ={a}^{\mathrm{2}} \\ $$$${x}_{{A}} ^{\mathrm{2}} −\mathrm{2}{bx}_{{A}} +{b}^{\mathrm{2}} +\left[\frac{\left({b}−{r}\:\mathrm{sin}\:\theta\right){x}_{{A}} }{{r}\:\mathrm{cos}\:\theta}−\frac{{s}^{\mathrm{2}} −{a}^{\mathrm{2}} +{b}^{\mathrm{2}} −{r}^{\mathrm{2}} }{\mathrm{2}{r}\:\mathrm{cos}\:\theta}\right]^{\mathrm{2}} ={a}^{\mathrm{2}} \\ $$$$\left[\mathrm{1}+\frac{\left({b}−{r}\:\mathrm{sin}\:\theta\right)^{\mathrm{2}} }{{r}^{\mathrm{2}} \:\mathrm{cos}^{\mathrm{2}} \:\theta}\right]{x}_{{A}} ^{\mathrm{2}} −\mathrm{2}\left[{b}+\frac{\left({b}−{r}\:\mathrm{sin}\:\theta\right)\left({s}^{\mathrm{2}} −{a}^{\mathrm{2}} +{b}^{\mathrm{2}} −{r}^{\mathrm{2}} \right)}{\mathrm{2}{r}^{\mathrm{2}} \:\mathrm{cos}^{\mathrm{2}} \:\theta}\right]{x}_{{A}} +\frac{\left({s}^{\mathrm{2}} −{a}^{\mathrm{2}} +{b}^{\mathrm{2}} −{r}^{\mathrm{2}} \right)^{\mathrm{2}} }{\mathrm{4}{r}^{\mathrm{2}} \:\mathrm{cos}^{\mathrm{2}} \:\theta}+{b}^{\mathrm{2}} −{a}^{\mathrm{2}} =\mathrm{0} \\ $$$$\Rightarrow{x}_{{A}} =\frac{\mathrm{1}}{\mathrm{1}+\frac{\left({b}−{r}\:\mathrm{sin}\:\theta\right)^{\mathrm{2}} }{{r}^{\mathrm{2}} \:\mathrm{cos}^{\mathrm{2}} \:\theta}}\left\{{b}+\frac{\left({b}−{r}\:\mathrm{sin}\:\theta\right)\left({s}^{\mathrm{2}} −{a}^{\mathrm{2}} +{b}^{\mathrm{2}} −{r}^{\mathrm{2}} \right)}{\mathrm{2}{r}^{\mathrm{2}} \:\mathrm{cos}^{\mathrm{2}} \:\theta}\pm\sqrt{\left[{b}+\frac{\left({b}−{r}\:\mathrm{sin}\:\theta\right)\left({s}^{\mathrm{2}} −{a}^{\mathrm{2}} +{b}^{\mathrm{2}} −{r}^{\mathrm{2}} \right)}{\mathrm{2}{r}^{\mathrm{2}} \:\mathrm{cos}^{\mathrm{2}} \:\theta}\right]^{\mathrm{2}} −\left[\mathrm{1}+\frac{\left({b}−{r}\:\mathrm{sin}\:\theta\right)^{\mathrm{2}} }{{r}^{\mathrm{2}} \:\mathrm{cos}^{\mathrm{2}} \:\theta}\right]\left[\frac{\left({s}^{\mathrm{2}} −{a}^{\mathrm{2}} +{b}^{\mathrm{2}} −{r}^{\mathrm{2}} \right)^{\mathrm{2}} }{\mathrm{4}{r}^{\mathrm{2}} \:\mathrm{cos}^{\mathrm{2}} \:\theta}+{b}^{\mathrm{2}} −{a}^{\mathrm{2}} \right]}\right\} \\ $$$${point}\:{B}: \\ $$$$\left({x}_{{B}} −{r}\:\mathrm{sin}\:\theta\right)^{\mathrm{2}} +\left({y}_{{B}} −{r}\:\mathrm{cos}\:\theta\right)^{\mathrm{2}} ={s}^{\mathrm{2}} \\ $$$$\left({x}_{{B}} +{a}\right)^{\mathrm{2}} +{y}_{{B}} ^{\mathrm{2}} ={b}^{\mathrm{2}} \\ $$$$−\left({a}+{r}\:\mathrm{sin}\:\theta\right)\left(\mathrm{2}{x}_{{B}} +{a}−{r}\:\mathrm{sin}\:\theta\right)−{r}\:\mathrm{cos}\:\theta\:\left(\mathrm{2}{y}_{{B}} −{r}\:\mathrm{cos}\:\theta\right)={s}^{\mathrm{2}} −{b}^{\mathrm{2}} \\ $$$$\mathrm{2}\left({a}+{r}\:\mathrm{sin}\:\theta\right)\:{x}_{{B}} +\mathrm{2}{r}\:\mathrm{cos}\:\theta\:{y}_{{B}} =−{s}^{\mathrm{2}} +{b}^{\mathrm{2}} −{a}^{\mathrm{2}} +{r}^{\mathrm{2}} \\ $$$$\Rightarrow{y}_{{B}} =\frac{−\mathrm{2}\left({a}+{r}\:\mathrm{sin}\:\theta\right){x}_{{B}} −{s}^{\mathrm{2}} +{b}^{\mathrm{2}} −{a}^{\mathrm{2}} +{r}^{\mathrm{2}} }{\mathrm{2}{r}\:\mathrm{cos}\:\theta} \\ $$$$\left({x}_{{B}} +{a}\right)^{\mathrm{2}} +\left[\frac{−\mathrm{2}\left({a}+{r}\:\mathrm{sin}\:\theta\right){x}_{{B}} −{s}^{\mathrm{2}} +{b}^{\mathrm{2}} −{a}^{\mathrm{2}} +{r}^{\mathrm{2}} }{\mathrm{2}{r}\:\mathrm{cos}\:\theta}\right]^{\mathrm{2}} ={b}^{\mathrm{2}} \\ $$$$\left({x}_{{B}} +{a}\right)^{\mathrm{2}} +\left[\frac{\left({a}+{r}\:\mathrm{sin}\:\theta\right){x}_{{B}} }{{r}\:\mathrm{cos}\:\theta}+\frac{{s}^{\mathrm{2}} −{b}^{\mathrm{2}} +{a}^{\mathrm{2}} −{r}^{\mathrm{2}} }{\mathrm{2}{r}\:\mathrm{cos}\:\theta}\right]^{\mathrm{2}} ={b}^{\mathrm{2}} \\ $$$$\left[\mathrm{1}+\frac{\left({a}+{r}\:\mathrm{sin}\:\theta\right)^{\mathrm{2}} }{{r}^{\mathrm{2}} \mathrm{cos}^{\mathrm{2}} \:\theta}\right]{x}_{{B}} ^{\mathrm{2}} +\mathrm{2}\left[{a}+\frac{\left({a}+{r}\:\mathrm{sin}\:\theta\right)\left({s}^{\mathrm{2}} −{b}^{\mathrm{2}} +{a}^{\mathrm{2}} −{r}^{\mathrm{2}} \right)}{\mathrm{2}{r}^{\mathrm{2}} \:\mathrm{cos}^{\mathrm{2}} \:\theta}\right]{x}_{{B}} +\frac{\left({s}^{\mathrm{2}} −{b}^{\mathrm{2}} +{a}^{\mathrm{2}} −{r}^{\mathrm{2}} \right)^{\mathrm{2}} }{\mathrm{4}{r}^{\mathrm{2}} \:\mathrm{cos}^{\mathrm{2}} \:\theta}+{a}^{\mathrm{2}} −{b}^{\mathrm{2}} =\mathrm{0} \\ $$$$\Rightarrow{x}_{{B}} =\frac{\mathrm{1}}{\mathrm{1}+\frac{\left({a}+{r}\:\mathrm{sin}\:\theta\right)^{\mathrm{2}} }{{r}^{\mathrm{2}} \mathrm{cos}^{\mathrm{2}} \:\theta}}\left\{−{a}−\frac{\left({a}+{r}\:\mathrm{sin}\:\theta\right)\left({s}^{\mathrm{2}} −{b}^{\mathrm{2}} +{a}^{\mathrm{2}} −{r}^{\mathrm{2}} \right)}{\mathrm{2}{r}^{\mathrm{2}} \:\mathrm{cos}^{\mathrm{2}} \:\theta}\pm\sqrt{\left[{a}+\frac{\left({a}+{r}\:\mathrm{sin}\:\theta\right)\left({s}^{\mathrm{2}} −{b}^{\mathrm{2}} +{a}^{\mathrm{2}} −{r}^{\mathrm{2}} \right)}{\mathrm{2}{r}^{\mathrm{2}} \:\mathrm{cos}^{\mathrm{2}} \:\theta}\right]^{\mathrm{2}} −\left[\mathrm{1}+\frac{\left({a}+{r}\:\mathrm{sin}\:\theta\right)^{\mathrm{2}} }{{r}^{\mathrm{2}} \mathrm{cos}^{\mathrm{2}} \:\theta}\right]\left[\frac{\left({s}^{\mathrm{2}} −{b}^{\mathrm{2}} +{a}^{\mathrm{2}} −{r}^{\mathrm{2}} \right)^{\mathrm{2}} }{\mathrm{4}{r}^{\mathrm{2}} \:\mathrm{cos}^{\mathrm{2}} \:\theta}+{a}^{\mathrm{2}} −{b}^{\mathrm{2}} \right]}\right\} \\ $$$$ \\ $$$${AB}={s}: \\ $$$$\left({x}_{{A}} −{x}_{{B}} \right)^{\mathrm{2}} +\left({y}_{{A}} −{y}_{{B}} \right)^{\mathrm{2}} ={s}^{\mathrm{2}} \\ $$$${x}_{{A}} ^{\mathrm{2}} +{y}_{{A}} ^{\mathrm{2}} +{x}_{{B}} ^{\mathrm{2}} +{y}_{{B}} ^{\mathrm{2}} −\mathrm{2}{x}_{{A}} {x}_{{B}} −\mathrm{2}{y}_{{A}} {y}_{{B}} ={s}^{\mathrm{2}} \\ $$$$\Rightarrow\left({a}+{x}_{{A}} \right)\left({b}−{x}_{{B}} \right)−{y}_{{A}} {y}_{{B}} =\frac{{s}^{\mathrm{2}} }{\mathrm{2}}+{ab} \\ $$$$…… \\ $$
Commented by ajfour last updated on 06/Apr/23
$${lengthy}\:{but}\:{you}\:{solved}\:{it},\:{sir}.\:{Very} \\ $$$${commendable}!\:{thank}\:{you}. \\ $$