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Question 20.8.3: Reduce the equation √3x+y+2=0 to the normal form x cos α+y s......

Reduce the equation \sqrt{3} x+y+2=0 to the normal form x \cos \alpha+y \sin \alpha=p , and hence find the values of \alpha and p .

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We have

\begin{aligned}\sqrt{3} x+y+2=0 \Rightarrow &   -\sqrt{3} x-y=2 \quad \text { [keeping constant +ve] } \\  \\\Rightarrow &   \left(\frac{-\sqrt{3}}{2}\right) x+\left(\frac{-1}{2}\right) y=1 \\  \\& \quad\left[\text { on dividing throughout by } \sqrt{(\sqrt{3})^{2}+1^{2}}\right] \\  \\\Rightarrow &   x \cos \alpha+y \sin \alpha=p, \\  \\& \text { where } \cos \alpha=\frac{-\sqrt{3}}{2}, \sin \alpha=\frac{-1}{2} \text { and } p=1 .\end{aligned}

Since \cos \alpha<0 and \sin \alpha<0 , \alpha lies in the third quadrant.

Now, \tan \alpha=\frac{\sin \alpha}{\cos \alpha}=\left(\frac{-1}{2}\right) \times\left(\frac{-2}{\sqrt{3}}\right)=\frac{1}{\sqrt{3}}=\tan \left(180^{\circ}+30^{\circ}\right)=\tan 210^{\circ} \\  \\ \Rightarrow   \alpha=210^{\circ} .

Thus, \alpha=210^{\circ} and p=1 .

Hence, the given equation in normal form is given by

x \cos 210^{\circ}+y \sin 210^{\circ}=1.

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