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Published byErnest Chapman Modified over 7 years ago

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How much paint do we need to paint all the rooms in our house? bedroom kitchen TV room

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Square Area = s 2 (s = side length) Rectangle Area = lw (l = length and w = width) Triangle Area = ½bh (b = base and h = height)

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You can justify the area formula for triangles as follows: The area of a triangle is half the area of a parallelogram with the same base and height. Area of a Parallelogram = bh Area of a Triangle = ½bh

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Be careful when identifying the height of a triangle! The height is NEVER a side of a triangle unless the triangle is RIGHT. hh h

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Ex 1: Find the area of.. a. A square whose sides have length 8 cm. 8 cm A = s 2 A = 8 2 A = 64 cm 2

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b. A rectangle whose length is 5 m and width is 11 m. 5 m 11 m A = lw A = (5)(11) A = 55 m 2 11 m 5 m

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c. A triangle whose side lengths are 3 in, 4 in, and 5 in. A = ½ (4)(3) A = ½ (12) A = 6 in 2 3 in 4 in 5 in

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Ex 2: Find the indicated side length. a. A square with area 256 in 2. 16 in A = s 2 256 = s 2 16 = s 16 in

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b. A rectangle with area 345 ft and length 15 ft. 15 ft 23 ft A = lw 345 = 15w 23 ft = w 23 ft 15 ft

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c. A triangle with area 12 mm and a base length of 6 mm. A = ½ bh 12 = ½ (6)h 12 = 3h 4 mm = h 6 mm 4 mm

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Parallelogram Area = bh (b = base and h = height) Trapezoid Area = ½ h (b 1 + b 2 ) Rhombus Area = ½d 1 d 2 (d = diagonal)

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You can justify the area formula for parallelograms as follows: h The area of a parallelogram is the area of a rectangle with the same base and height. Area of Parallelogram = bh

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Ex 3: Find the area of parallelogram ABCD A BC D E F12 16 9 12 Method 1 Use AB as the base and BE as the height.

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Ex 3: Find the area of parallelogram ABCD A B C D E F12 16 9 12 Method 2 Use AD as the base and CF as the height. You get the same answer.

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Ex 4: Find the area of trapezoid WXYZ. X(1, 1)W(8, 1) Z(5, 5)Y(2, 5) Count the blocks for height, base 1, and base 2.

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Ex 5:The area of a trapezoid is 135 cm 2, height is 9, and one bases is 11. Find the other base.

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Ex 6: Find the area of the rhombus. 9 9 12

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Ex 7: The area of a rhombus is 40 in 2 and one of the diagonals is 8 in. Find the other diagonal.

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Ex 8: Find the area if the radius. Leave your answer in terms of pi unless stated otherwise. Circle Area =

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