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Trigonometric Equations — MATHS STD 11 Science — Question

Rajasthan BoardEnglish MediumSTD 11 ScienceMATHSTrigonometric Equations3 Marks
Question
Solve the following equation:
$2\sin^{2}\text{x}+\sqrt{3}\cos\text{x}+1=0$
✓

Answer

We have,
$2\sin^{2}\text{x}+\sqrt{3}\cos\text{x}+1=0$
$\Rightarrow2(1-\cos^{2}\text{x})+\sqrt{3}\cos\text{x}+1=0$
$\Rightarrow2\cos^{2}\text{x}-\sqrt{3}\cos\text{x}-3=0$
factorise it,we get,
$\Rightarrow2\cos^{2}\text{x}-2\sqrt{3}\cos\text{x}+\sqrt{3}\cos\text{x}-3=0$
$\Rightarrow2\cos\text{x}(\cos\text{x}-\sqrt{3})+\sqrt{3}(\cos\text{x}-\sqrt{3})=0$
$\Rightarrow(2\cos\text{x}+\sqrt{3})(\cos\text{x}-\sqrt{3})=0$
$\Rightarrow\text{Either}$ 
$\cos\text{x}=-\frac{\sqrt{3}}{2}$ or $\cos\text{x}=\sqrt{3}$ [This is not possible as$-1<\cos\text{x}<1$]
$\Rightarrow\cos\text{x}=\cos\Big(\pi-\frac{\pi}{6}\Big)$
$\Rightarrow\cos\text{x}=\cos\frac{5\pi}{6}$
$\Rightarrow\text{x}=2\text{n}\pi\pm\frac{5\pi}{6},\text{n}\in\text{z}$

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