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MHT CET · Maths · Application of Derivatives

All the points on the curve \(y^{2}=4 a|x+a \sin (x / a)|\), where the tangent is parallel to the axis of \(x\) are lies on

  1. A circle
  2. B parabola
  3. C straight line
  4. D None of these
Verified Solution

Answer & Solution

Correct Answer

(B) parabola

Step-by-step Solution

Detailed explanation

\(y^{2}=4 a\left[x+a \sin \left(\frac{x}{a}\right)\right]\)...(i)
\(\therefore 2 y \frac{d y}{d x}=4 a\left[1+\cos \left(\frac{x}{a}\right)\right]\)...(ii)
If tangent is parallel to \(x\) -axis, then \(\frac{d y}{d x}=0\)
So, from Eq. (i), we get \(\cos \left(\frac{x}{a}\right)=-1\)
\(\therefore\) \(
\sin \left(\frac{x}{a}\right)=0
\)
On putting this value in Eq. (i), we get \(y^{2}=4 a(x+0) \Rightarrow y^{2}=4 a x\)
So, all the points on the curve
\(
y^{2}=4 a\left(x+a \sin \frac{x}{a}\right)
\)
where the tangent is parallel to the \(x\) -axis are lies on parabola.