Euclidean Distance • Manhattan Distance • Midpoint
\( d = \sqrt{(x_2-x_1)^2 + (y_2-y_1)^2} \)
Where:
This formula calculates the straight-line distance between two points in a 2D coordinate plane.
Example: For points A(3, 4) and B(7, 1):
\( d = \sqrt{(7-3)^2 + (1-4)^2} = \sqrt{16 + 9} = \sqrt{25} = 5 \)
Thus, the distance between points A and B is 5 units.
Coordinate geometry combines algebra and geometry by representing geometric figures using coordinates. It allows us to analyze geometric properties using algebraic equations and formulas. The Cartesian coordinate system provides a framework for describing positions and relationships between points, lines, and shapes.
The Euclidean distance formula is derived from the Pythagorean theorem:
This calculates the straight-line distance between two points in a 2D plane.
Coordinate geometry connects to several important concepts:
Direct straight-line distance between two points.
Sum of absolute differences: |x₂-x₁| + |y₂-y₁|
Coordinates of point halfway between two points.
What is the distance between points A(2, 3) and B(6, 7)?
The answer is B) 5.66 units. Using the distance formula: d = √[(x₂-x₁)² + (y₂-y₁)²] = √[(6-2)² + (7-3)²] = √[16 + 16] = √32 ≈ 5.66 units.
The distance formula is a direct application of the Pythagorean theorem. We create a right triangle where the horizontal leg is the difference in x-coordinates (6-2=4) and the vertical leg is the difference in y-coordinates (7-3=4). The hypotenuse of this triangle is the distance between the points. So d = √(4² + 4²) = √32 ≈ 5.66.
Distance Formula: d = √[(x₂-x₁)² + (y₂-y₁)²]
Pythagorean Theorem: c² = a² + b²
Cartesian Coordinates: (x, y) position in 2D plane
• Always subtract coordinates in consistent order
• Square both differences before adding
• Take square root of the sum
• Visualize the right triangle formed by the points
• Check if your answer is reasonable compared to coordinate differences
• Subtracting in wrong order: (x₁-x₂) instead of (x₂-x₁)
• Forgetting to square the differences
• Adding before squaring instead of after
Given points A(-3, 5) and B(7, -1), find the midpoint, slope of the line connecting them, and explain what the slope tells us about the line's direction.
Step 1: Find the midpoint using the midpoint formula: M = ((x₁+x₂)/2, (y₁+y₂)/2)
M = ((-3+7)/2, (5+(-1))/2) = (4/2, 4/2) = (2, 2)
Step 2: Find the slope using the slope formula: m = (y₂-y₁)/(x₂-x₁)
m = (-1-5)/(7-(-3)) = -6/10 = -3/5 = -0.6
Step 3: Interpret the slope: Since the slope is negative (-0.6), the line falls from left to right. The magnitude of 0.6 means that for every 1 unit moved to the right, the line drops 0.6 units vertically.
The midpoint formula averages the x-coordinates and y-coordinates separately to find the center point. The slope formula measures the rate of change of y with respect to x. A negative slope indicates a decreasing relationship between x and y, meaning as x increases, y decreases. The slope value of -0.6 means the line has a gentle downward incline.
Midpoint: Point equidistant from both endpoints
Slope: Measure of steepness and direction of a line
Direction: Positive slope rises, negative slope falls
• Midpoint = average of coordinates
• Slope = rise over run
• Negative slope means falling line
• Plot points to visualize the line before calculating
• Remember: slope = (change in y)/(change in x)
• Mixing up x and y coordinates in formulas
• Forgetting parentheses when subtracting negative numbers
• Confusing slope sign interpretation
Q: Why is the distance formula related to the Pythagorean theorem? They seem like completely different concepts.
A: The distance formula is actually a direct application of the Pythagorean theorem! When you have two points in a coordinate plane, you can imagine drawing a right triangle where:
• The horizontal leg has length |x₂ - x₁| (the difference in x-coordinates)
• The vertical leg has length |y₂ - y₁| (the difference in y-coordinates)
• The hypotenuse is the straight-line distance between the points
According to the Pythagorean theorem: c² = a² + b², where c is the hypotenuse. Substituting our legs: d² = (x₂ - x₁)² + (y₂ - y₁)². Taking the square root gives us the distance formula: d = √[(x₂ - x₁)² + (y₂ - y₁)²].
Q: What's the difference between Euclidean and Manhattan distance, and when would I use each?
A: Euclidean distance measures the straight-line distance between two points, while Manhattan distance measures the sum of absolute differences along each axis (like navigating city blocks).
Euclidean Distance: d = √[(x₂-x₁)² + (y₂-y₁)²] - Used when movement is unrestricted and can occur in any direction. Common in physics, engineering, and geometric applications.
Manhattan Distance: d = |x₂-x₁| + |y₂-y₁| - Used when movement is restricted to perpendicular directions. Common in urban planning, computer science (especially in grid-based algorithms), and machine learning for feature spaces.
For example, if you're calculating the shortest path for a drone flying between two points, use Euclidean distance. If you're calculating travel distance through a city grid, use Manhattan distance.