Talk:Section formula

Someone Deleted this

Coordinates of centroid

Centroid of a triangle

The centroid of a triangle is the intersection of the medians and divides each median in the ratio ${\textstyle 2:1}$. Let the vertices of the triangle be $A(x_{1},y_{1})$, ${\textstyle B(x_{2},y_{2})}$ and ${\textstyle C(x_{3},y_{3})}$. So, a median from point A will intersect BC at ${\textstyle \left({\frac {x_{2}+x_{3}}{2}},{\frac {y_{2}+y_{3}}{2}}\right)}$. Using the section formula, the centroid becomes:

$$G=\left({\frac {x_{1}+x_{2}+x_{3}}{3}},{\frac {y_{1}+y_{2}+y_{3}}{3}}\right)$$

Coordinates of incenter

Let the sides of a triangle be ${\textstyle a}$, ${\textstyle b}$ and ${\textstyle c}$ its vertices are ${\textstyle A(x_{1},y_{1})}$, ${\textstyle B(x_{2},y_{2})}$ and ${\textstyle C(x_{3},y_{3})}$. The Incentre (intersection of the angle bisectors) divides the angle bisectors in the ratio ${\textstyle (b+c):a}$, ${\textstyle (a+c):b}$ and ${\textstyle (a+b):c}$. An angle bisector also divides the opposite side in the ratio of the adjacent sides (Angle bisector theorem). So they meet at ${\textstyle \left({\frac {bx_{2}+cx_{3}}{b+c}},{\frac {by_{2}+cy_{3}}{b+c}}\right)}$. Thus, the incenter is

$$I=\left({\frac {ax_{1}+bx_{2}+cx_{3}}{a+b+c}},{\frac {ay_{1}+by_{2}+cy_{3}}{a+b+c}}\right)$$

This is essentially the weighted average of the vertices.

Shubhrajit Sadhukhan (talk) 13:25, 7 November 2020 (UTC)