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Fill in the number of sides

Understand and calculate polygon and circle areas with formulas and examples. Practice finding areas of triangles, parallelograms, and circles.

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Fill in the number of sides

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  1. Fill in the number of sides Find the sum of the measures of the interior angles of a Nonagon. 3 7 9 6 5 (9 – 2)180 = 7(180) = 1,2600 12 4 10 8 03/12/08

  2. Ch. 7-6 Areas of Polygons Area is the number of square units the figure encloses. It is flat – 2 dimensional – cm2 Example: If you were ordering carpet for a rectangular room, you would need to know the area of the room. Important Formulas for finding area: Parallelogram: A = bh where b is the base and h is the height Triangle: A = 1/2bh where b is the base and h is the height Trapezoid: A = 1/2h(b1 + b2)

  3. Example 1: Find the area of each figures below. Use the appropriate formula. Area of a Triangle = ½ bh The base is 7 and the height is 3. 6 cm. 3 cm. 7 cm. A = ½ (7)(3) = 10.5 cm.2 Area of a Parallelogram = bh The base is 12 and the height is 20. 22 cm. 20 cm. A = (12)(20) = 240 cm.2 12 cm.

  4. Example 2: Find the area of each figure below. Use the appropriate formula. 6 m. Area of a Trapezoid = ½h(b1 + b2) The bases are 6 and 3 and the height is 4. 4 m. A = ½ (4)(3 + 6) = 18 m.2 3 m. Example 3: Use the area formulas to solve for each unknown below. a.) The area of a parallelogram is 221 yd.2 Its height is 13 yd. What is the length of its corresponding base? Use the Area formula for a parallelogram, plug in what you know and solve for the unknown. 221 = 13b Divide both sides by 13 b = 17 yd.

  5. b.) A triangle has area 85 cm.2 Its base is 5 cm. What is its height? Use the Area formula for a triangle, plug in what you know and solve for the unknown. 85 = ½(5)h Multiply 5 * 1/2 85 = 5/2h Divide by 5/2, since it is a fraction you are really multiplying by the reciprocal! 2/5 * 85 = 5/2h x 2/5 34 cm. = h

  6. Ch. 7-7 Circumference and Area of a Circle Important formulas when dealing with circles: Circumference = diameter multiplied by pi or 3.14 C = Circumference = 2 multiplied by the radius multiplied by pi or 3.14 C = Area of a Circle = pi multiplied by the radius squared A = Chord Parts of a Circle: Radius Circumference Diameter

  7. Example 1: Find the circumference and area of each object below. Use the formulas given. Find the circumference and area of the basketball hoop C = 45 * 3.14 = 141.3 cm. 45 cm. A = 3.14 * (22.5)2 = 1589.6 cm.2 Find the circumference and area of the tire C = 12 * 3.14 = 37.68 in. A = 3.14 * (6)2 = 113.04 in.2 12 in.

  8. Example 2: Find the area of each irregular figure below. You are going to have to use multiple area formulas. First find the area of the rectangle. A = length multiplied by width 10 in. Area of the rectangle = 7 * 10 = 70 in. 2 7 in. Next find the area of the semi-circle A = Area of Semi-Circle = ½ (3.14)(5)2 = 39.25 in.2 Last, add the two areas together: 39.25 + 70 = 109.25 in.2

  9. Example 3: Find the area of each irregular figure below. You are going to have to use multiple area formulas. 6.6 m. 13.2 m. First find the area of the rectangle. A = length multiplied by width 19.8 m. Area of the rectangle = 19.8 * 13.2 = 261.36 m. 2 Next find the area of the semi-circle A = Area of Semi-Circle = ½ (3.14)(6.6)2 = 68.39 m.2 Last need to subtract the area of the semi-circle from the area of the rectangle 261.36 – 68.39 = 192.97 m.2

  10. HW – Pg. 331 • PG 331 #1-4 all, 6-10 even • PG 338 #4-22 even

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