Question:

The slopes of the focal chords of the parabola $y^{2}=32 x$, which are tangents to the circle $x^{2}+y^{2}=4$, are

Updated On: Dec 15, 2023
  • $\frac{1}{2}, \frac{-1}{2}$
  • $\frac{1}{\sqrt{3}}, \frac{-1}{\sqrt{3}}$
  • $\frac{1}{\sqrt{15}}, \frac{-1}{\sqrt{15}}$
  • $\frac{2}{\sqrt{5}}, \frac{-2}{\sqrt{5}}$
Hide Solution
collegedunia
Verified By Collegedunia

The Correct Option is C

Solution and Explanation

Given equation of circle is $x^{2}+y^{2}=(2)^{2}$ $\therefore$ The equation of tangent to the circle is $y=m x \pm 2 \sqrt{1+m^{2}}\left(\because y=m x \pm r \sqrt{1+m^{2}}\right)$ Also, equation of parabola is $y^{2}=32 x$ $\therefore$ Focus of parabola is $(8,0)$ Since, the line passes through focus $(8,0)$. $\therefore 0=8 m \pm 2 \sqrt{1+m^{2}}$ $\Rightarrow -4 m=\pm \sqrt{1+m^{2}}$ $\Rightarrow 16 m^{2}=1+m^{2}$ $\Rightarrow 15 m^{2}=1$ $\Rightarrow m^{2}=\frac{1}{15}$ $\Rightarrow m=\pm \frac{1}{\sqrt{15}}$
Was this answer helpful?
2
0

Concepts Used:

Straight lines

A straight line is a line having the shortest distance between two points. 

A straight line can be represented as an equation in various forms,  as show in the image below:

 

The following are the many forms of the equation of the line that are presented in straight line-

1. Slope – Point Form

Assume P0(x0, y0) is a fixed point on a non-vertical line L with m as its slope. If P (x, y) is an arbitrary point on L, then the point (x, y) lies on the line with slope m through the fixed point (x0, y0) if and only if its coordinates fulfil the equation below.

y – y0 = m (x – x0)

2. Two – Point Form

Let's look at the line. L crosses between two places. P1(x1, y1) and P2(x2, y2)  are general points on L, while P (x, y) is a general point on L. As a result, the three points P1, P2, and P are collinear, and it becomes

The slope of P2P = The slope of P1P2 , i.e.

\(\frac{y-y_1}{x-x_1} = \frac{y_2-y_1}{x_2-x_1}\)

Hence, the equation becomes:

y - y1 =\( \frac{y_2-y_1}{x_2-x_1} (x-x1)\)

3. Slope-Intercept Form

Assume that a line L with slope m intersects the y-axis at a distance c from the origin, and that the distance c is referred to as the line L's y-intercept. As a result, the coordinates of the spot on the y-axis where the line intersects are (0, c). As a result, the slope of the line L is m, and it passes through a fixed point (0, c). The equation of the line L thus obtained from the slope – point form is given by

y – c =m( x - 0 )

As a result, the point (x, y) on the line with slope m and y-intercept c lies on the line, if and only if

y = m x +c