7.2-Section Formula
7.2-Section Formula Important Formulae
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Grade 10 → Math → Coordinate Geometry → 7.2-Section Formula
- Apply and derive section formula in order to divide the line segment in a given ratio
- Apply distance and section formula in order to determine the vertices/diagonals/mid points of given geometrical shapes.
The section formula is a key concept in coordinate geometry used to determine the coordinates of a point that divides a line segment into a given ratio. This formula is particularly useful when working with points in a Cartesian plane.
If we have two points, $A(x_1, y_1)$ and $B(x_2, y_2)$, and a point $P$ divides the line segment $AB$ in the ratio $m:n$, then the coordinates of point $P(x, y)$ can be calculated using the section formula.
The formula for the coordinates of point $P$ is given by:
$P\left(x, y\right) = \left(\frac{{mx_2 + nx_1}}{{m + n}}, \frac{{my_2 + ny_1}}{{m + n}}\right)$
Here:
- $P(x, y)$ = Coordinates of the point dividing the segment
- $A(x_1, y_1)$ = Coordinates of the first point
- $B(x_2, y_2)$ = Coordinates of the second point
- $m$ = Ratio of division (part from $B$)
- $n$ = Ratio of division (part from $A$)
To illustrate the section formula, let’s consider an example. Suppose we have two points:
Point $A(2, 3)$ and Point $B(8, 5)$, and we want to find the coordinates of point $P$ that divides the segment $AB$ in the ratio $3:2$.
Using the section formula:
$P\left(x, y\right) = \left(\frac{{3 \cdot 8 + 2 \cdot 2}}{{3 + 2}}, \frac{{3 \cdot 5 + 2 \cdot 3}}{{3 + 2}}\right)$
Calculating the $x$-coordinate:
$x = \frac{{24 + 4}}{{5}} = \frac{{28}}{{5}} = 5.6$
Now, calculating the $y$-coordinate:
$y = \frac{{15 + 6}}{{5}} = \frac{{21}}{{5}} = 4.2$
Therefore, the coordinates of point $P$ are $P\left(5.6, 4.2\right)$.
In the case where point $P$ divides the segment externally, the section formula is slightly modified. If point $P$ divides the line segment $AB$ externally in the ratio $m:n$, the coordinates can be calculated as:
$P\left(x, y\right) = \left(\frac{{mx_2 - nx_1}}{{m - n}}, \frac{{my_2 - ny_1}}{{m - n}}\right)$
For example, if we take the same points $A(2, 3)$ and $B(8, 5)$ and consider point $P$ dividing the segment externally in the ratio $3:2$, we can apply the external section formula:
$P\left(x, y\right) = \left(\frac{{3 \cdot 8 - 2 \cdot 2}}{{3 - 2}}, \frac{{3 \cdot 5 - 2 \cdot 3}}{{3 - 2}}\right)$
Calculating the $x$-coordinate:
$x = \frac{{24 - 4}}{{1}} = 20$
Calculating the $y$-coordinate:
$y = \frac{{15 - 6}}{{1}} = 9$
Thus, the coordinates of point $P$ in the external division case are $P(20, 9)$.
The section formula is extensively used in coordinate geometry for finding points that partition line segments, making it essential for various geometric constructions and proofs.