Find the third vertex of triangle whose centroid is origin and two vertices are (2,4,6) and (0,-2,-5).

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(2,4,6)

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Concept understanding — Coordinate Geometry

Coordinate Geometry: Where Algebra Meets Geometry

Imagine you're telling a friend where you left your book in a library. You don't say "near the window" — you say "third shelf, second row, fourth book from the left." You're using numbers to pin down an exact location.

Coordinate geometry does the same thing, but for points on a flat surface. It gives every point a precise address — a pair of numbers — so we can describe shapes, distances, and positions using algebra.

The Big Idea

Before coordinate geometry, geometry was about drawing shapes and proving things with logic alone. Algebra was about numbers and equations. These two worlds seemed separate.

Then René Descartes (a French mathematician) had a simple but revolutionary idea: draw two perpendicular number lines that cross at zero. Now every point on the plane has a unique pair of numbers — its coordinates.

That's it. That's the entire foundation.

The Coordinate System

Take a horizontal line — call it the x-axis. Take a vertical line — call it the y-axis. They cross at a point called the origin, labelled $O$ .

Any point $P$ is located by two numbers:

Its x-coordinate: how far right (positive) or left (negative) from the origin
Its y-coordinate: how far up (positive) or down (negative) from the origin

We write this as an ordered pair: $(x, y)$ .

Note

The order matters. $(3, 5)$ is not the same point as $(5, 3)$ . The first number is always the horizontal position; the second is always the vertical.

A Concrete Example

Plot the point $A(2, 3)$ :

Start at the origin $(0, 0)$ .
Move 2 units to the right along the x-axis.
From there, move 3 units up (parallel to the y-axis).
Mark the point.

Now plot $B(-1, 4)$ :

Start at the origin.
Move 1 unit left (negative x-direction).
Move 4 units up.
Mark the point.

Every point on the plane has exactly one such address. And every pair of numbers corresponds to exactly one point. This one-to-one matching is what makes coordinate geometry powerful.

The Four Quadrants

The axes divide the plane into four regions, called quadrants:

Quadrant	x-sign	y-sign	Example
I	$+$	$+$	$(2, 3)$
II	$-$	$+$	$(-1, 4)$
III	$-$	$-$	$(-3, -2)$
IV	$+$	$-$	$(5, -1)$

Points on the axes themselves (where either coordinate is zero) don't belong to any quadrant.

Why This Matters

Once every point has a number address, we can:

Calculate distances between points using the Pythagorean theorem
Find midpoints by averaging coordinates
Describe lines with equations like $y = mx + c$
Solve geometric problems using algebra instead of drawing

Important

The distance between two points $(x_1, y_1)$ and $(x_2, y_2)$ is:

$d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}$

This is just the Pythagorean theorem in disguise.

The Precise Statement

Coordinate geometry (also called analytic geometry) is the study of geometry using a coordinate system. It establishes a correspondence between:

Points on a plane and ordered pairs of real numbers
Geometric figures (lines, circles, curves) and algebraic equations …

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The centroid of a triangle is the average of its vertices' coordinates. Given the centroid is the origin and two vertices, we find the third vertex by setting up equations for each coordinate, resulting in the third vertex being $\boxed{(-2, -2, -1)}$ .

In coordinate geometry, the centroid of a triangle is a fundamental point. It's the point where the three medians of the triangle intersect. A median connects a vertex to the midpoint of the opposite side. The beauty of the centroid is that its coordinates are simply the arithmetic mean (average) of the coordinates of the three vertices. This holds true whether the triangle is in 2D (with $x$ and $y$ coordinates) or in 3D (with $x, y,$ and $z$ coordinates).

The intuition behind this is that the centroid represents the "center of mass" of the triangle if its mass were uniformly distributed along its perimeter or area. Averaging the coordinates effectively finds this central balancing point.

Let's apply this concept to find the missing vertex.

Identify the given information:

We are given:
- The centroid of the triangle, $G = (0,0,0)$ (the origin).
- Two vertices, $A = (2,4,6)$ and $B = (0,-2,-5)$ .
- We need to find the third vertex, let's call it $C = (x_3, y_3, z_3)$ .
Recall the Centroid Formula for 3D:

If the three vertices of a triangle are $A=(x_1, y_1, z_1)$ , $B=(x_2, y_2, z_2)$ , and $C=(x_3, y_3, z_3)$ , then the coordinates of its centroid $G=(x_G, y_G, z_G)$ are given by:
$x_G = \frac{x_1+x_2+x_3}{3}$
Substitute the known values into the formula:

We have $x_1=2, y_1=4, z_1=6$ for vertex $A$ .

We have $x_2=0, y_2=-2, z_2=-5$ for vertex $B$ .

We have $x_G=0, y_G=0, z_G=0$ for the centroid $G$ .

We need to find $x_3, y_3, z_3$ .

For the $x$ -coordinate:

$0 = \frac{2+0+x_3}{3}$ …

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Q.Find the third vertex of triangle whose centroid is origin and two vertices are (2,4,6)(2,4,6)(2,4,6) and (0,−2,−5)(0,-2,-5)(0,−2,−5).

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Q.Find the third vertex of triangle whose centroid is origin and two vertices are $(2,4,6)$ and $(0,-2,-5)$ .

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