Sigma Percentile
JEE Advanced 2000
LEVELBoard

Animated Solution for Mathematics - Straight Lines: The incentre of the triangle with vertices and is

Select Answer:

Visualized Solution

Plotting the Base Vertices

  • Let's visualize the given vertices on the Cartesian plane.
  • is at the origin.
  • lies on the positive -axis.

Completing the Triangle

  • The third vertex is .
  • Connect the vertices to form .

Calculating Side Length

  • Distance formula:

Calculating Sides and

Identifying the Triangle Type

  • We observe that .
  • Since all three sides are equal in length, is an equilateral triangle.

The Equilateral Shortcut

  • General Incentre formula:
  • In an equilateral triangle, all centers (Centroid, Incentre, Circumcentre, Orthocentre) coincide.
  • Therefore, Incentre = Centroid.

Applying the Centroid Formula

  • Centroid
  • We will substitute the coordinates of , , and .

Computing the -coordinate

Computing the -coordinate

Final Answer and Visualization

  • The Incentre is .
  • Key Takeaway: Always check if a triangle is equilateral or right-angled before applying complex coordinate geometry formulas.

The Sigma Insight: Centroid, Incenter, Orthocenter, and Circumcenter

Solution Diagram

Analyzing the Geometry

Welcome, future engineer. Today, we are going to solve a problem that seems like a standard coordinate geometry exercise but is actually a profound lesson in observation.
We are given three vertices: , , and . When you see these coordinates, don't just jump into the formula. Stop, breathe, and visualize.
Plotting these points on the Cartesian plane reveals a beautiful, symmetric structure. Point is at the origin, and sits on the -axis. Point is perched above, creating a triangle.

Calculating Side Lengths

Now, let's calculate the side lengths. Using the distance formula , we find the lengths of the sides:
This is the 'Aha!' moment. All sides are equal, confirming that we have an equilateral triangle.

The Master Equation

In the world of geometry, symmetry is a gift. For an equilateral triangle, the incentre, centroid, circumcentre, and orthocentre all collapse into a single point.
This means we don't need the complex incentre formula. We can simply find the centroid, which is the average of the coordinates:
Plugging in our values, we calculate the coordinates:

Final Result

Our incentre is located at the point:
This problem teaches us that the most efficient path is often found by observing the properties of the figure before applying the formulas. Keep this mindset, and you will conquer the JEE.

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