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Objective

Find the area of triangles and trapezoids

Vocabulary

Trapezoid

A quadrilateral with one pair of parallel sides

Example 1 Find the Area of a Triangle

Example 2 Find the Area of a Trapezoid

Example 3 Use a Formula to Estimate Area

Find the area of the triangle

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Write formula for area of triangle

Replace b (for base) with 9 cm

Replace h (height) with 3.2 cm

(9 cm)(3.2 cm)

Find the area of the triangle

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Multiply numbers(9 cm)(3.2 cm)

A = 14.4

Multiply units

cm2

Answer:

Find the area of the triangle

Answer: A = 13.5 ft2

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Find the area of the trapezoid

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Write the formula for area of a trapezoid

Replace h (for height) with 3 m

(3 m)

Replace b1 (for base) with 7.6 m

(7.6 m

Replace b2 (for base) with 4 m

+ 4 m)

Find the area of the trapezoid

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Follow Order of Operations

P E MD AS(3 m)(7.6 m + 4 m)

(3 m)(11.6 m)Multiply numbers

A = 17.5Multiply units

meters2

Answer:

Find the area of the trapezoid

Answer: A = 61.5 cm2

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GEOGRAPHY The shape of the state of Montana resembles a trapezoid. Estimate its area in square miles.

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Write the formula for area of a trapezoid

Replace h (for height) with 285 mi

(285 mi)

Replace b1 (for base) with 479 mi

(479 mi

Replace b2 (for base) with 542 mi

+ 542 mi)

GEOGRAPHY The shape of the state of Montana resembles a trapezoid. Estimate its area in square miles.

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(285 mi) (479 mi + 542 mi)

Follow Order of Operations

P E MD AS

(285 mi) (1,021 mi)Multiply numbers

A = 145.492.5

Multiply units

miles2

Answer:

PAINTING The diagram below is of a canvas resembling a trapezoid that will be painted. In order to determine how much paint will be needed, estimate the area of the canvas in square feet.

Answer: A = 150 ft2

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Assignment

Lesson 11:5Area of Triangles and

Trapezoids4 - 14 All