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Area and Perimeter of Trapezoids

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What if you were given a trapezoid and the size of its two bases as well as its height? How could you find the total distance around the trapezoid and the amount of space it takes up? After completing this Concept, you'll be able to use the formulas for the perimeter and area of a trapezoid to solve problems like this.

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Area and Perimeter of Trapezoids CK-12

Guidance

A trapezoid is a quadrilateral with one pair of parallel sides. The parallel sides are called the bases and we will refer to the lengths of the bases as b_1 and b_2 . The perpendicular distance between the parallel sides is the height of the trapezoid. The area of a trapezoid is A=\frac{1}{2} h(b_1+b_2) where h is always perpendicular to the bases.

Example A

Find the area of the trapezoid below.

A & = \frac{1}{2} (11)(14+8)\\A & = \frac{1}{2} (11)(22)\\A & = 121 \ units^2

Example B

Find the area of the trapezoid below.

A & = \frac{1}{2} (9)(15+23)\\A & = \frac{1}{2} (9)(38)\\A & = 171 \ units^2

Example C

Find the perimeter and area of the trapezoid.

Even though we are not told the length of the second base, we can find it using special right triangles. Both triangles at the ends of this trapezoid are isosceles right triangles, so the hypotenuses are 4 \sqrt{2} and the other legs are of length 4.

P &= 8+4\sqrt{2}+16+4\sqrt{2} && A=\frac{1}{2}(4)(8+16)\\P &= 24+8\sqrt{2} \approx 35.3 \ units && A=48 \ units^2

Area and Perimeter of Trapezoids CK-12

Guided Practice

Find the area of the following shapes. Round your answers to the nearest hundredth.

Answers

Use the formula for the area of a trapezoid.

1. \frac{1}{2}(18)(41+21)= 558 \ units^2 .

2. \frac{1}{2}(7)(14+8)= 77 \ units^2 .

3. \frac{1}{2}(5)(16+9)= 62.5 \ units^2 .

Practice

Find the area and perimeter of the following shapes. Round your answers to the nearest hundredth.

Find the area of the following trapezoids.

  1. Trapezoid with bases 3 in and 7 in and height of 3 in.
  2. Trapezoid with bases 6 in and 8 in and height of 5 in.
  3. Trapezoid with bases 10 in and 26 in and height of 2 in.
  4. Trapezoid with bases 15 in and 12 in and height of 10 in.
  5. Trapezoid with bases 4 in and 23 in and height of 21 in.
  6. Trapezoid with bases 9 in and 4 in and height of 1 in.
  7. Trapezoid with bases 12 in and 8 in and height of 16 in.
  8. Trapezoid with bases 26 in and 14 in and height of 19 in.

Use the given figures to answer the questions.

  1. What is the perimeter of the trapezoid?
  2. What is the area of the trapezoid?

  1. What is the perimeter of the trapezoid?
  2. What is the area of the trapezoid?

  1. What is the perimeter of the trapezoid?
  2. What is the area of the trapezoid?

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