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Geometry: Coordinate geometry & distance formula

Grade 10 · Math · Free lesson

Hey there! Today we are going to explore how to find the exact distance between any two points on a flat grid, just like finding the shortest path on a map!

Imagine you are looking at a treasure map laid out on a grid. If you want to walk from one point to another, you could walk horizontally and then vertically, forming a right-angled triangle.

board

By connecting our two points with a straight line, we create the hypotenuse of a right-angled triangle. We can use the famous Pythagorean Theorem (a² + b² = c²) to help us find this diagonal distance!

A (1, 1) B (3, 3)

The Distance Formula is just a neat package for this idea! It is written as: d = √((x₂ - x₁)² + (y₂ - y₁)²). We subtract the x-coordinates to find the width, subtract the y-coordinates to find the height, square them both, add them, and take the square root.

d = √[ (x₂ - x₁)² + (y₂ - y₁)² ] Horizontal change (run) Vertical change (rise)
✏️ Worked example

Find the distance between the points P(2, 3) and Q(6, 6).

  1. Identify the coordinates: (x₁, y₁) = (2, 3) and (x₂, y₂) = (6, 6).
  2. Find the horizontal distance: x₂ - x₁ = 6 - 2 = 4.
  3. Find the vertical distance: y₂ - y₁ = 6 - 3 = 3.
  4. Plug these values into the distance formula: d = √((4)² + (3)²).
  5. Simplify the squares: d = √(16 + 9) = √(25).
  6. Take the square root to get the final answer: d = 5 units.
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