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# Area and Perimeter of Trapezoids

## Area is the height times the average of the bases while the perimeter is the sum of the sides.

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Area and Perimeter of Trapezoids

### Area and Perimeter of Trapezoids

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 b1\begin{align*}b_1\end{align*} and b2\begin{align*}b_2\end{align*}. The perpendicular distance between the parallel sides is the height of the trapezoid. The area of a trapezoid is A=12h(b1+b2)\begin{align*}A=\frac{1}{2} h(b_1+b_2)\end{align*} where h\begin{align*}h\end{align*} is always perpendicular to the bases.

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?

### Examples

#### Example 1

Find the area of the trapezoid.

Use the formula for the area of a trapezoid.

12(18)(41+21)=558 units2\begin{align*}\frac{1}{2}(18)(41+21)= 558 \ units^2\end{align*}

#### Example 2

Find the area of the trapezoid. Round your answers to the nearest hundredth.

Use the formula for the area of a trapezoid.

12(5)(16+9)=62.5 units2\begin{align*}\frac{1}{2}(5)(16+9)= 62.5 \ units^2\end{align*}

#### Example 3

Find the area of the trapezoid.

AAA=12(11)(14+8)=12(11)(22)=121 units2\begin{align*}A & = \frac{1}{2} (11)(14+8)\\ A & = \frac{1}{2} (11)(22)\\ A & = 121 \ units^2\end{align*}

#### Example 4

Find the area of the trapezoid.

AAA=12(9)(15+23)=12(9)(38)=171 units2\begin{align*}A & = \frac{1}{2} (9)(15+23)\\ A & = \frac{1}{2} (9)(38)\\ A & = 171 \ units^2\end{align*}

#### Example 5

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 42\begin{align*}4 \sqrt{2}\end{align*} and the other legs are of length 4.

PP=8+42+16+42=24+8235.3 unitsA=12(4)(8+16)A=48 units2\begin{align*}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\end{align*}

### Review

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?

To see the Review answers, open this PDF file and look for section 10.5.

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Color Highlighted Text Notes

### Vocabulary Language: English Spanish

area

The amount of space inside a figure. Area is measured in square units.

isosceles trapezoid

An isosceles trapezoid is a trapezoid where the non-parallel sides are congruent.

midsegment (of a trapezoid)

A line segment that connects the midpoints of the non-parallel sides.

perimeter

The distance around a shape. The perimeter of any figure must have a unit of measurement attached to it. If no specific units are given (feet, inches, centimeters, etc), write units.

trapezoid

A quadrilateral with exactly one pair of parallel sides.