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
  1. \(p \in(-\pi, 0)\)
  2. \(p \in\left(\frac{-\pi}{2}, \frac{\pi}{2}\right)\)
  3. \(p \in(0, \pi)\)
  4. \(p \in(0,2 \pi)\)

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)

Practice more Quadratic Equation questions on Aicharya