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MJ2

MJ2. Ch 11.5 Area of Triangles & Trapezoids. 7 ½ yd. 6 ½ yd. 8 yd. Bellwork. Calculate the area of the parallelogram. 7 ½ yd. 6 ½ yd. 8 yd. Bellwork Solution. A = bh. A = 8(6.5). A = 52yd 2. Assignment Review. Text p. 485 # 10 - 19. Before we begin….

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MJ2

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  1. MJ2 Ch 11.5 Area of Triangles & Trapezoids

  2. 7 ½ yd 6 ½ yd 8 yd Bellwork • Calculate the area of the parallelogram

  3. 7 ½ yd 6 ½ yd 8 yd Bellwork Solution A = bh A = 8(6.5) A = 52yd2

  4. Assignment Review • Text p. 485 # 10 - 19

  5. Before we begin… • Please take out your notebook and get ready to work… • In the last lesson we looked at the area of a parallelogram… • In today’s lesson we will look at the area of triangles and trapezoids…the formulas for these geometric shapes are related to the area of a parallelogram…

  6. Objective 11.5 • Students will find the area of triangles & trapezoids.

  7. Vocabulary • Base – the base of a triangle can be any one of its sides • Height – the height of a triangle is the distance from the base to the opposite vertex Height Vertex Base

  8. Area of a Triangle • The formula for the area of a triangle is: A = ½bh • This is related to the area of a parallelogram as follows… • A parallelogram can be cut by a diagonal into 2 separate triangles, therefore the formula for area of a triangle is ½ of the area of a parallelogram

  9. Triangles • If a parallelogram is cut in ½ by a diagonal 2 separate triangles are created. • Therefore, the area of a triangle is ½ the area of a parallelogram

  10. Area of Triangles • Again, you will use the formula method to calculate the area of a triangle • The formula method demonstrates what you know and minimizes errors. • You will be required to use this method for all assignments • Let’s look at an example…

  11. 6.5 m 10 m Example A = ½ bh 1. Write the formula A = ½ (10)(6.5) 2. Substitute A = 5(6.5) 3. Do the math A = 32.5 m2 Your answer is squared because you are measuring 2 dimensions

  12. 3.2 cm 9 cm Your Turn • In the notes section of your notebook draw & label the triangle and then calculate area using the formula A= ½ bh

  13. 3.2 cm 9 cm Your Turn Solution A = ½ bh 1. Write the formula A = ½ (9)(3.2) 2. Substitute A = (4.5)(3.2) 3. Do the math A = 14.4 cm2

  14. Trapezoids • The area for a trapezoid can be related to the area of a parallelogram • If a line is drawn through a parallelogram it cuts the parallelogram into 2 trapezoids

  15. Vocabulary • A trapezoid has 2 bases called b1 and b2 • It doesn’t matter which one you call b1 or b2 • The height is the distance between the 2 bases b2 height b1

  16. Area of a Trapezoid • To calculate the area of a trapezoid use the formula: A = ½ h(b1 + b2) • Again, you will use the formula method which demonstrates what you know and minimizes errors • Let’s see what it looks like…

  17. 7 ft 8 ft 15.6 ft Area of Trapezoids A = ½ 8(7 + 15.6) A = ½ h(b1 + b2) 1. Write the formula 2. Substitute A = ½ (8)(22.6) 3. Do the math A = 4(22.6) A = 90.4 ft2

  18. 4 m 3 m 7.6 m Your Turn • In the notes section of your notebook calculate the area of the trapezoid using the formula method and the formula A = ½ h(b1 + b2)

  19. 4 m 3 m 7.6 m Your Turn Solution A = ½ h(b1 + b2) 1. Write the formula A = ½ 3(4 + 7.6) 2. Substitute A = ½ (3)(11.6) 3. Do the math A = ½ (34.8) A = 17.4 m2

  20. Comments • Like a triangle, when finding the area of trapezoids, sometimes you are given extra information • The purpose is to see if you know what a base and a height are… • In a trapezoid the height is the distance between the two bases. • The right angle symbol is the clue to what the height is and where the bases are…

  21. 8 cm 7 cm 7 cm 6 cm 12.5 cm Example This is the height The right angle symbol is the clue to where the height is These are the bases because the height is the distance between the two bases

  22. Summary • In the notes section of your notebook summarize the key concepts covered in today’s lesson • Today we discussed • Area of Triangles & Trapezoids • What method will you use to demonstrate what you have learned? • What symbol is the clue to where the height is?

  23. Assignment • Text p. 491 # 8 – 15 Reminder: • This assignment is due tomorrow • I do not accept late assignments • Draw & label the picture and show how you got your answer using the formula method. • Answers only will not be accepted for a grade

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