Question:

If the three lines $x - 3y = p, \,ax + 2y = q$ and $ax + y = r$ form a right-angled triangle then :

Updated On: Oct 10, 2024
  • $a^2 - 9a + 18 = 0$
  • $a^2 - 6a - 12 = 0$
  • $a^2 - 6a - 18 = 0$
  • $a^2 - 9a + 12 = 0$
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The Correct Option is A

Solution and Explanation

Since three lines $x - 3y = p$,
$ax + 2y = q$ and $ax + y = r$
form a right angled triangle
$\therefore$ product of slopes of any two lines $= -1$
Suppose $ax + 2y = q$ and $x - 3y = pare \,\bot$ to each other.
$\therefore \quad \frac{-a}{2}\times\frac{1}{3} = -1 \Rightarrow a = 6$
Now, consider option one by one
$a = 6$ satisfies only option
$\therefore$ Required answer is $a^{2} - 9a +18 = 0$
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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