Distance and Midpoint Formulas
Working with coordinates in the plane
Distance and Midpoint Formulas
Distance Formula
The distance between two points and :
Derivation: This comes from the Pythagorean Theorem!
Midpoint Formula
The midpoint between two points and :
Memory aid: Average the x-coordinates, average the y-coordinates.
Applications
Perimeter: Add distances between consecutive vertices
Proving shapes:
- Square: All 4 sides equal, diagonals equal
- Rectangle: Opposite sides equal, diagonals equal
- Rhombus: All 4 sides equal
- Isosceles triangle: Two sides equal
Segment Partitioning
To find a point that divides a segment in ratio :
Use weighted average based on the ratio
Coordinate Proof Strategy
- Place figure on coordinate plane strategically
- Use distance/midpoint formulas
- Show required properties
📚 Practice Problems
1Problem 1easy
❓ Question:
Find the distance between points A(3, 4) and B(7, 1).
💡 Show Solution
Step 1: Recall the distance formula: d = √[(x₂ - x₁)² + (y₂ - y₁)²]
Step 2: Identify the coordinates: Point A: (x₁, y₁) = (3, 4) Point B: (x₂, y₂) = (7, 1)
Step 3: Substitute into the formula: d = √[(7 - 3)² + (1 - 4)²] d = √[4² + (-3)²] d = √[16 + 9] d = √25 d = 5
Answer: The distance is 5 units
2Problem 2easy
❓ Question:
Find the distance between points and .
💡 Show Solution
Use the distance formula:
Answer: 5 units
3Problem 3easy
❓ Question:
Find the midpoint of the segment connecting (-2, 5) and (6, -3).
💡 Show Solution
Step 1: Recall the midpoint formula: M = ((x₁ + x₂)/2, (y₁ + y₂)/2)
Step 2: Identify the coordinates: Point 1: (x₁, y₁) = (-2, 5) Point 2: (x₂, y₂) = (6, -3)
Step 3: Calculate x-coordinate of midpoint: x_m = (-2 + 6)/2 = 4/2 = 2
Step 4: Calculate y-coordinate of midpoint: y_m = (5 + (-3))/2 = 2/2 = 1
Step 5: Write the midpoint: M = (2, 1)
Answer: The midpoint is (2, 1)
4Problem 4medium
❓ Question:
Find the midpoint of the segment connecting and .
💡 Show Solution
Use the midpoint formula:
Answer:
5Problem 5medium
❓ Question:
Point M(4, 7) is the midpoint of segment AB. If A is at (2, 3), find the coordinates of point B.
💡 Show Solution
Step 1: Recall the midpoint formula: M = ((x₁ + x₂)/2, (y₁ + y₂)/2)
Step 2: Set up equations using given information: M(4, 7) and A(2, 3) 4 = (2 + x_B)/2 7 = (3 + y_B)/2
Step 3: Solve for x-coordinate of B: 4 = (2 + x_B)/2 8 = 2 + x_B x_B = 6
Step 4: Solve for y-coordinate of B: 7 = (3 + y_B)/2 14 = 3 + y_B y_B = 11
Step 5: Verify: Midpoint = ((2 + 6)/2, (3 + 11)/2) = (8/2, 14/2) = (4, 7) ✓
Answer: Point B is at (6, 11)
6Problem 6medium
❓ Question:
A circle has center C(2, -1) and passes through point P(5, 3). Find the radius of the circle.
💡 Show Solution
Step 1: Understand the problem: The radius is the distance from center to any point on the circle So radius = distance from C to P
Step 2: Use the distance formula: d = √[(x₂ - x₁)² + (y₂ - y₁)²]
Step 3: Substitute C(2, -1) and P(5, 3): r = √[(5 - 2)² + (3 - (-1))²] r = √[3² + 4²] r = √[9 + 16] r = √25 r = 5
Step 4: Recognize the Pythagorean triple: This is a 3-4-5 right triangle
Answer: The radius is 5 units
7Problem 7hard
❓ Question:
Prove that the triangle with vertices , , and is a right triangle.
💡 Show Solution
Strategy: Show that the sides satisfy the Pythagorean Theorem.
Find all three side lengths:
: from to
: from to
: from to
Check Pythagorean Theorem:
Since , the triangle is a right triangle.
Answer: Yes, it's a right triangle (in fact, a 5-12-13 right triangle)
8Problem 8hard
❓ Question:
Points A(-3, 2), B(5, 8), and C(x, y) form a right triangle with the right angle at B. If C is on the x-axis, find the coordinates of C.
💡 Show Solution
Step 1: Understand the constraints:
- Right angle at B
- C is on the x-axis, so y-coordinate = 0: C(x, 0)
- Need to find x
Step 2: Use perpendicular slopes: If angle at B is 90°, then AB ⊥ BC Slopes must multiply to -1
Step 3: Find slope of AB: m_AB = (8 - 2)/(5 - (-3)) m_AB = 6/8 = 3/4
Step 4: Find slope of BC: m_BC = (0 - 8)/(x - 5) m_BC = -8/(x - 5)
Step 5: Set up perpendicularity condition: m_AB × m_BC = -1 (3/4) × (-8/(x - 5)) = -1
Step 6: Solve for x: (3/4) × (-8)/(x - 5) = -1 -24/(4(x - 5)) = -1 -24 = -4(x - 5) -24 = -4x + 20 -44 = -4x x = 11
Step 7: Verify the perpendicularity: m_AB = 3/4 m_BC = -8/(11 - 5) = -8/6 = -4/3 Product: (3/4) × (-4/3) = -12/12 = -1 ✓
Answer: Point C is at (11, 0)
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