JEE Main 2006
- Exam
- JEE Main
- Year
- 2006
- Subject
- Mathematics
- Chapter
- Parabola
JEE Main 2006 · Mathematics · Parabola
The locus of the vertices of the family of parabolas y=(a^3...
The locus of the vertices of the family of parabolas is
Options
- A
- B
- C
- D
Correct answer
A.
Step-by-step solution
Parabola:
Vertex: \begin{aligned}& \alpha=\frac{-a^2 / 2}{2 a^3 / 3}=-\frac{3}{4 a}, \beta=\frac{-\left(\frac{a^4}{4}+4 \cdot \frac{a^3}{3} \cdot 2 a\right)}{4 \frac{a^3}{3}}=-\frac{-\left(\frac{1}{4}+\frac{8}{3}\right) a^4}{\frac{4}{3} a^3}\\
& =-\frac{35}{12} \frac{a}{4} \times3=-\frac{35}{16}a \\
& \alpha \beta=-\frac{3}{4 a} \left(-\frac{35}{16}\rright)a=\frac{105}{64} .
\end{aligned}$$