Question:

The vertices of ΔPQR are P (2, 1), Q (-2, 3) and R (4, 5). Find equation of the median through the vertex R.

Updated On: Oct 25, 2023
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Solution and Explanation

It is given that the vertices of ΔPQR are P (2, 1), Q (2, 3), and R (4, 5).
Let RL be the median through vertex R.
Accordingly, L is the mid-point of PQ.
By mid-point formula, the coordinates of point L are given by \((\frac {2-2}{2},\frac {1+3}{2})=(0,2)\)
\(y-y_1 = \frac {y_2-y_1}{x_2-x_1}(x-x_1)\)

ΔPQR with vertices P (2,1), Q (2,3) and R (4,5)

It is known that the equation of the line passing through points (x1, y1) and (x2, y2) is.
So, the equation of RL can be determined by substituting (x1, y1) = (4, 5) and (x2, y2) = (0, 2).
Hence, 
\(y-5=\frac {2-5}{0-4}(x-4)\)
⇒ \(y-5=\frac {-3}{-4}(x-4)\)
⇒ \(4(y-5)=3(x-4)\)
⇒ \(4y-20=3x-12\)
⇒ \(3x-4y+8=0\)

Thus, the required equation of the median through vertex R is \(3x-4y+8 = 0\).

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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