If the roots of the given equation \((\cos p-1) x^2+(\cos p) x+\sin p=0\) are real, then
If the roots of the given equation \((\cos p-1) x^2+(\cos p) x+\sin p=0\) are real, then
- \(p \in(-\pi, 0)\)
- \(p \in\left(\frac{-\pi}{2}, \frac{\pi}{2}\right)\)
- \(p \in(0, \pi)\)
- \(p \in(0,2 \pi)\)
Solution
\((\cos p-1) x^2+(\cos p) x+\sin p=0\)
Since, roots are real
\(\begin{array}{rlrl}
\Rightarrow & \Delta \geq 0 \Rightarrow b^2-4 a c \geq 0 \\
& (\cos p)^2-4(\cos p-1) (\sin p) \geq 0 \\
& \cos ^2 p \geq 0 \text { and }(\cos p-1) \leq 0 \forall P \in \mathbf{R} \\
& \therefore \sin p \geq 0 \\
& \therefore p \in(0, \pi)
\end{array}\)
Hence, option (c) is correct.
Asked in: AP EAMCET 2020 (18 Sep Shift 2)
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