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JEE Main 2024
Properties of Triangle
Properties of Triangle
Hard

Question

In the figure, θ1+θ2=π2\theta_{1}+\theta_{2}=\frac{\pi}{2} and 3(BE)=4(AB)\sqrt{3}(\mathrm{BE})=4(\mathrm{AB}). If the area of CAB\triangle \mathrm{CAB} is 2332 \sqrt{3}-3 unit 2{ }^{2}, when θ2θ1\frac{\theta_{2}}{\theta_{1}} is the largest, then the perimeter (in unit) of CED\triangle \mathrm{CED} is equal to _________.

Answer: 1

Solution

We have, θ1+θ2=π2\theta_1+\theta_2=\frac{\pi}{2} and 3(BE)=4AB\sqrt{3}(B E)=4 A B Let AB=xA B=x unit AC=xtanθ1ED=xtanθ2BE=BD+DE\begin{aligned} & A C=x \tan \theta_1 \\\\ & E D=x \tan \theta_2 \\\\ & B E=B D+D E \end{aligned} 43x=x(tanθ1+tanθ2)[3BE=4AB]43=tanθ1+tan(π2θ1)[θ1+θ2=π2]\begin{array}{rlrl} & \Rightarrow \frac{4}{\sqrt{3}} x =x\left(\tan \theta_1+\tan \theta_2\right) {[\because \sqrt{3} B E=4 A B]} \\\\ & \Rightarrow \frac{4}{\sqrt{3}}=\tan \theta_1+\tan \left(\frac{\pi}{2}-\theta_1\right) {\left[\because \theta_1+\theta_2=\frac{\pi}{2}\right]} \end{array} tanθ1+cotθ1=43=3+13tanθ1=3 or θ1=π3 and θ2=π6orθ1=π6 and θ2=π3\begin{aligned} & \Rightarrow \tan \theta_1+\cot \theta_1=\frac{4}{\sqrt{3}}=\sqrt{3}+\frac{1}{\sqrt{3}} \\\\ & \Rightarrow \tan \theta_1=\sqrt{3} \text { or } \theta_1=\frac{\pi}{3} \text { and } \theta_2=\frac{\pi}{6} \\\\ & \operatorname{or} \theta_1=\frac{\pi}{6} \text { and } \theta_2=\frac{\pi}{3} \end{aligned} θ2θ1\because \frac{\theta_2}{\theta_1} is largest θ1=π6 and θ2=π3\therefore \theta_1=\frac{\pi}{6} \text { and } \theta_2=\frac{\pi}{3}  Area of CAB=12×x×xtanθ1x2tanθ12=233x2=2(233)tanπ6=1263 x=33\begin{aligned} & \text { Area of } \triangle C A B=\frac{1}{2} \times x \times x \tan \theta_1 \\\\ & \Rightarrow \frac{x^2 \tan \theta_1}{2}=2 \sqrt{3}-3 \\\\ & \Rightarrow x^2=\frac{2(2 \sqrt{3}-3)}{\tan \frac{\pi}{6}}=12-6 \sqrt{3} \\\\\ & \Rightarrow x=3-\sqrt{3} \end{aligned}  Also, CE=x2+x2tan2π3=(33)×2=623\text { Also, } C E=\sqrt{x^2+x^2 \tan ^2 \frac{\pi}{3}}=(3-\sqrt{3}) \times 2=6-2 \sqrt{3} Perimeter of CED\triangle C E D =CD+DE+CE=(33)+(33)tanπ3+623=33+333+623=6\begin{aligned} & =C D+D E+C E \\\\ & =(3-\sqrt{3})+(3-\sqrt{3}) \tan \frac{\pi}{3}+6-2 \sqrt{3} \\\\ & =3-\sqrt{3}+3 \sqrt{3}-3+6-2 \sqrt{3}=6 \end{aligned}

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