The sides of a triangle are $\sin \theta, \cos \theta$ and $\sqrt{1+\sin \theta \cos \theta}$ for some $0…

The sides of a triangle are $\sin \theta, \cos \theta$ and $\sqrt{1+\sin \theta \cos \theta}$ for some $0 \lt \theta \lt \frac{\pi}{2}$, then the greatest angle of a triangle is
  1. $\frac{\pi}{3}$
  2. $\frac{2 \pi}{3}$
  3. $\frac{\pi}{6}$
  4. $\frac{5 \pi}{6}$

Solution

$\mathrm{a}=\sin \theta, \mathrm{b}=\cos \theta \text { and } \mathrm{c}=\sqrt{1+\sin \theta \cos \theta}$
Since $\sqrt{1+\sin \theta \cos \theta}$ is greater than $\sin \theta$ and $\cos \theta$. $\therefore \quad C$ is the greatest angle, $\begin{aligned} & \therefore \quad \cos C \\ & \therefore \quad \\ & \quad=\frac{a^2+b^2-c^2}{2 a b} \\ & \\ & \quad=-\frac{1}{2}=\cos 120^{\circ} \\ & \therefore \quad C \end{aligned}$

Asked in: MHT CET 2024 (09 May Shift 1)

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