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WBJEE · Maths · Trigonometric Equations

If the equation \(\sin ^4 x-(p+2) \sin ^2 x-(p+3)=0\) has a solution, the \(p\) must lie in the interval

  1. A \([-3,-2]\)
  2. B \((-3,-2)\)
  3. C \((2,3)\)
  4. D \([-5,-3]\)
Verified Solution

Answer & Solution

Correct Answer

(B) \((-3,-2)\)

Step-by-step Solution

Detailed explanation

\(\begin{aligned} & \sin ^2 x=\frac{(P+2) \pm \sqrt{(P+2)^2+4.1(P+3)}}{2.1} \\ & =\frac{(P+2) \pm \sqrt{P^2+4 p+4+4 p+12}}{2} \\ & =\frac{(P+2) \pm \sqrt{(P+4)^2}}{2} \\ & =\frac{2 p+6}{2}=P+3 \\ & =\sin ^2 x \in[0,1] \\ 0 & \leq P+3 \leq 1 \\ & -3 \leq P \leq-2\end{aligned}\)