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MHT CET · Maths · Trigonometric Equations

If a \(\cos 2 \theta+b \sin 2 \theta=c\) has \(\alpha\) and \(\beta\) as its roots, then the value of \(\tan \alpha+\tan \beta\) is

  1. A \(\frac{2 b}{c+a}\)
  2. B \(\frac{2 a}{b+c}\)
  3. C \(\frac{b}{c+a}\)
  4. D \(\frac{a}{b+c}\)
Verified Solution

Answer & Solution

Correct Answer

(A) \(\frac{2 b}{c+a}\)

Step-by-step Solution

Detailed explanation

\(\begin{aligned} & \text { We have, } \mathrm{a} \cos 2 \theta+\mathrm{b} \sin 2 \theta=\mathrm{c} \\ & \Rightarrow \mathrm{a}\left(\frac{1-\tan ^2 \theta}{1+\tan ^2 \theta}\right)+\mathrm{b}\left(\frac{2 \tan \theta}{1+\tan ^2 \theta}\right)=\mathrm{c} \\ & \Rightarrow \mathrm{a}-\mathrm{a} \tan ^2 \theta+2 \mathrm{~b} \tan \theta=\mathrm{c}+\mathrm{c} \tan ^2 \theta \\ & \Rightarrow-(\mathrm{a}+\mathrm{c}) \tan ^2 \theta+2 \mathrm{~b} \tan \theta+(\mathrm{a}-\mathrm{c})=0 \\ & \therefore \quad \tan \alpha+\tan \beta=-\frac{2 \mathrm{~b}}{-(\mathrm{c}+\mathrm{a})}=\frac{2 \mathrm{~b}}{\mathrm{c}+\mathrm{a}}\end{aligned}\)