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Introduction

Learn how to apply the distance formula to solve perimeter and area problems for polygons. Find the lengths of sides, calculate perimeter and area, and avoid common errors.

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Introduction

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  1. Introduction The distance formula can be used to find solutions to many real-world problems. In the previous lesson, the distance formula was used to find the distance between two given points. In this lesson, the distance formula will be applied to perimeter and area problems. A polygon is a two-dimensional figure formed by three or more segments. Sometimes we need to calculate the perimeter or distance around a polygon, as well as find the area or the amount of space inside the boundary of a polygon. The distance formula is a valuable tool for both of these calculations. 6.2.2: Calculating Perimeter and Area

  2. Key Concepts Situations where you would need to calculate perimeter include finding the amount of linear feet needed to fence a yard or a garden, determining the amount of trim needed for a room, or finding the amount of concrete needed to edge a statue. Perimeter is the sum of the lengths of all the sides of a polygon. The final answer must include the appropriate label (units, feet, inches, meters, centimeters, etc.). 6.2.2: Calculating Perimeter and Area

  3. Key Concepts, continued Sometimes the answer is not a whole number. If it is not, you must simplify the radical and then approximate the value. 6.2.2: Calculating Perimeter and Area

  4. Key Concepts, continued Calculating area is necessary when finding the amount of carpeting needed for a room in your home, or to determine how large a garden will be. The area of a triangle is found using the formula . The height of a triangle is the perpendicular distance from the third vertex to the base of the triangle. 6.2.2: Calculating Perimeter and Area

  5. Key Concepts, continued It may be necessary to determine the equation of the line that represents the height of the triangle before calculating the area. For an example of this, see Example 3 in the Guided Practice. Determining the lengths of the base and the height is necessary if these lengths are not stated in the problem. The final answer must include the appropriate label (units2, feet2, inches2, meters2, centimeters2, etc.). 6.2.2: Calculating Perimeter and Area

  6. Key Concepts, continued 6.2.2: Calculating Perimeter and Area

  7. Key Concepts, continued By definition, rectangles have adjacent sides that are perpendicular. The area of a rectangle is found using the formula Area = (base)(height). The lengths of the base and height are found using the distance formula. The final answer must include the appropriate label (units2, feet2, inches2, meters2, centimeters2, etc.). 6.2.2: Calculating Perimeter and Area

  8. Key Concepts, continued 6.2.2: Calculating Perimeter and Area

  9. Common Errors/Misconceptions forgetting to simplify radicals incorrectly simplifying radicals adding x-values and y-values rather than subtracting them when using the distance formula incorrectly finding the height of a triangle 6.2.2: Calculating Perimeter and Area

  10. Guided Practice Example 2 Quadrilateral ABCD has vertices A (–3, 0), B (2, 4), C (3, 1), and D (–4, –3). Calculate the perimeter of the quadrilateral. 6.2.2: Calculating Perimeter and Area

  11. Guided Practice: Example 2, continued Calculate the length of each side of the quadrilateral using the distance formula. Calculate the length of . Distance formula Substitute (–3, 0) and (2, 4). Simplify as needed. The length of is units. 6.2.2: Calculating Perimeter and Area

  12. Guided Practice: Example 2, continued Calculate the length of . Distance formula Substitute (2, 4) and (3, 1). Simplify as needed. The length of is units. 6.2.2: Calculating Perimeter and Area

  13. Guided Practice: Example 2, continued Calculate the length of . Distance formula Substitute (3, 1) and (–4, –3). Simplify as needed. The length of is units. 6.2.2: Calculating Perimeter and Area

  14. Guided Practice: Example 2, continued Calculate the length of . Distance formula Substitute (–4, –3) and (–3, 0). Simplify as needed. The length of is units. 6.2.2: Calculating Perimeter and Area

  15. Guided Practice: Example 2, continued Calculate the perimeter of quadrilateral ABCD. Find the sum of the sides of the quadrilateral. perimeter = AB + BC + CD + DA The perimeter ofquadrilateralABCD is units. ✔ 6.2.2: Calculating Perimeter and Area

  16. Guided Practice: Example 2, continued 6.2.2: Calculating Perimeter and Area

  17. Guided Practice Example 3 Triangle ABC has vertices A (1, –1), B (4, 3), and C (5, –3). Calculate the area of triangle ABC. 6.2.2: Calculating Perimeter and Area

  18. Guided Practice: Example 3, continued Find the equation of the line that represents the base of the triangle. Let be the base. Calculate the slope of the equation that represents side . 6.2.2: Calculating Perimeter and Area

  19. Guided Practice: Example 3, continued Slope formula Substitute (1, –1) and (5, –3). Simplify as needed. The slope of the equation the represents side is . 6.2.2: Calculating Perimeter and Area

  20. Guided Practice: Example 3, continued Write the equation of the line that represents side . y – y1 = m(x – x1)Point-slope formula Substitute for m. Substitute (1, –1) for (x1, y1) Simplify. 6.2.2: Calculating Perimeter and Area

  21. Guided Practice: Example 3, continued Distribute over (x – 1). Subtract 1 from both sides. The equation of the line that represents the base of the triangle is . 6.2.2: Calculating Perimeter and Area

  22. Guided Practice: Example 3, continued Find the equation of the line that represents the height of the triangle. The equation of the line that represents the height is perpendicular to the base; therefore, the slope of this line is the opposite reciprocal of the base. The slope of the line representing the height is 2. 6.2.2: Calculating Perimeter and Area

  23. Guided Practice: Example 3, continued y– y1 = m(x – x1)Point-slopeform y – y1= 2(x – x1) Substitute 2 for m. y – (3) = 2(x – (4)) Substitute (4, 3) for (x1, y1). y – 3 = 2(x – 4) Simplify. y – 3 = 2x – 8 Distribute2 over (x – 4). y = 2x – 5 Add 3 to both sides. The equation of the line that represents the height of the triangle is y= 2x – 5. 6.2.2: Calculating Perimeter and Area

  24. Guided Practice: Example 3, continued Find the point of intersection of the line representing the height and the line representing the base of the triangle. Set the equation of the line representing the base and the equation of the line representing the height equal to each other to determine the point of intersection. 6.2.2: Calculating Perimeter and Area

  25. Guided Practice: Example 3, continued Set the equations equal to each other. Add to both sides. Subtract 2x from both sides. Divide both sides by . The point of intersection has an x-value of . 6.2.2: Calculating Perimeter and Area

  26. Guided Practice: Example 3, continued Substitute into either equation to find the y-value. y= 2x– 5Equation of the line representing height Substitute for x. Simplify. Solve for y. 6.2.2: Calculating Perimeter and Area

  27. Guided Practice: Example 3, continued The point of intersection has a y-value of . The point of intersection is . 6.2.2: Calculating Perimeter and Area

  28. Guided Practice: Example 3, continued Calculate the length of the base, , of the triangle. Distance formula Substitute (1, –1) and (5, –3). Simplify as needed. The length of is units. 6.2.2: Calculating Perimeter and Area

  29. Guided Practice: Example 3, continued Calculate the length of the height from point B to the point of intersection. Distance formula Substitute (4, 3) and . Simplify as needed. 6.2.2: Calculating Perimeter and Area

  30. Guided Practice: Example 3, continued The length of the height is units. 6.2.2: Calculating Perimeter and Area

  31. Guided Practice: Example 3, continued Calculate the area of triangle ABC. Area formula for triangles Substitute the lengths of the height and the base of the triangle. Simplify as needed. 6.2.2: Calculating Perimeter and Area

  32. Guided Practice: Example 3, continued = 11 The area of triangle ABC is 11 square units. ✔ 6.2.2: Calculating Perimeter and Area

  33. Guided Practice: Example 3, continued 6.2.2: Calculating Perimeter and Area

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