Q94 / 160 · TS EAMCET 2020 (11 Sep Shift 2) · Mathematics
If all the vertices of an equilateral triangle lie on the parabola $y^2=16 x$ and one of them coincides with the vertex of that parabola, then the length of the side of that triangle is
- Correct answerA$32 \sqrt{3}$
- B$16 \sqrt{3}$
- C$8 \sqrt{3}$
- D32
Solution
Given equation of parabola, $y^2=16 x$ and all the vertices are of an equilateral triangle with one of them coincides with the vertex of parabola

Since, given parabola is symmetrical about $X$-axis So, $\angle A O M=30^{\circ}$ In $\triangle A O M, \tan 30^{\circ}=\frac{A M}{O M}=\frac{8 t}{4 t^2} \Rightarrow \frac{1}{\sqrt{3}}=\frac{2}{t} \Rightarrow$ $t=2 \sqrt{3}$ $\therefore$ Coordinate of point $A$ lying on parabola is $\left(4(2 \sqrt{3})^2, 8(2 \sqrt{3})\right) \equiv(48,16 \sqrt{3})$ $\therefore \text { Distance } O A=\sqrt{\left(x_A-x_0\right)^2+\left(y_A-y_0\right)^2}$ $=\sqrt{(48-0)^2+(16 \sqrt{3}-0)^2}$ $O A=32 \sqrt{3}$ $\therefore$ Length of the side of equilateral triangle $=32 \sqrt{3}$.

Since, given parabola is symmetrical about $X$-axis So, $\angle A O M=30^{\circ}$ In $\triangle A O M, \tan 30^{\circ}=\frac{A M}{O M}=\frac{8 t}{4 t^2} \Rightarrow \frac{1}{\sqrt{3}}=\frac{2}{t} \Rightarrow$ $t=2 \sqrt{3}$ $\therefore$ Coordinate of point $A$ lying on parabola is $\left(4(2 \sqrt{3})^2, 8(2 \sqrt{3})\right) \equiv(48,16 \sqrt{3})$ $\therefore \text { Distance } O A=\sqrt{\left(x_A-x_0\right)^2+\left(y_A-y_0\right)^2}$ $=\sqrt{(48-0)^2+(16 \sqrt{3}-0)^2}$ $O A=32 \sqrt{3}$ $\therefore$ Length of the side of equilateral triangle $=32 \sqrt{3}$.
Hence, the correct answer is option: 'A'.