# Area: Triangles and Trapezoids Lesson 10-2 p.509

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Area: Triangles and Trapezoids Lesson 10-2 p.509
Start the Bellwork Quiz. Have your HW, red pen, and book on your desk. Area: Triangles and Trapezoids Lesson 10-2 p.509

Triangles When finding the area of triangles, remember that a triangle is half of a parallelogram.

Triangles Now you can see why the formula for the area of a triangle makes sense: A = bh or A = bh 2

Triangles Let’s look at an example: A = bh = 4 (5) = 20 2 2 2
or 10 ft2 5 feet 4 feet

Try This Find the areas: 7 miles 3 ft. 5 mi. 12 in. 6 miles

Try This Find the areas: 7 miles 3 ft. 5 mi. 12 in. 6 miles 216 in2 or

Try This Find the areas: 7 miles 3 ft. 5 mi. 12 in. 6 miles 216 in2 or

Trapezoids Trapezoids have different formula. It looks like this:
A = h (b1 + b2) or A = h(b1 + b2) 2 b1 h b2

Trapezoids A = h (b1 + b2) or A = h(b1 + b2) 2
Note that there are 2 bases—base 1 and base 2. The formula takes the average of the two bases multiplied by the height. b1 h b2

Trapezoids Let’s try an example: A = h (b1 + b2) A = 3.5 (4 + 6) 2 2
A = 3.5 (5) = 17.5 ft2 4 ft 3.5 ft 6 feet

Try This Find the area: 24 mm 12 mm 33 mm

Try This Find the area: 24 mm 12 mm 342 mm2 33 mm

Try This Find the area: 4.5 feet 2 feet 4 feet

Try This Find the area: 4.5 feet 2 feet 13 ft2 4 feet

Example Some shapes look unusual, but when you remember just 3 formulas, you can calculate the area. Which two shapes do you see in the figure at the left?

Example There is a square (parallelogram) and a triangle. To find the area, first find the area of the parallelogram and then add it to the area of the triangle.

Example The square has an area of A = bh or 3 (3) or 9 ft2.
The triangle has an area of A = ½ bh or ½ (3) (2) or 3 ft2. The total area if or 12 ft2 3 ft 2 ft

Try This Find the area: 6 cm 6 cm 4 cm 8 cm

Try This Here is a hint: 6 cm 6 cm 4 cm 8 cm

Try This Here is a hint: For the rectangle: A = bh A = 6 (4) = 24 cm2
For the trapezoid: A = ½ h (b1 + b2) A = ½ (2) (4 + 6) A = 10 cm2 Total area = = 34 cm2 6 cm 6 cm 4 cm 8 cm

Try This Is there another way to divide this up? 6 cm 6 cm 4 cm 8 cm

Try This How about like this: 6 cm 6 cm 4 cm 8 cm

Try This How about like this: 6 cm For the rectangle:
A = bh = 8 (4) = 32 cm2 For the triangle: A = ½ bh = ½ (2) (2) = 2 cm2 The total area is or 34 cm2 6 cm 4 cm 8 cm

Agenda PA#38 Pp #8-16 even, 17, 19