## Trapezoids

The last family of quadrilaterals are the outcasts. They"re different from the remainder of the quadrilaterals, sort of like the socially awkward guest in ~ the square party.You are watching: How many pairs of parallel sides are in a trapezoid

While the rest of them have actually their congruent sides and also angles to chitchat about, this quadrilaterals simply hang by the snack bar. Every as soon as in a while, they could strike up a conversation with a lonesome polygon that happens to wander over, however it never ever lasts long and they simply go ago to uncomfortably staring at your feet.

A **trapezoid** is a quadrilateral with *only one* collection of parallel sides. They absolutely *cannot* have actually two sets of parallel sides. So when trapezoids begin their very own party after gift kicked out of the square party, we can be details that rectangles, squares, and also parallelograms will certainly not it is in on the guest list. Take that, suckers.

### Sample Problem

Is this square a trapezoid?

How numerous pairs that parallel lines perform you see? The top and also bottom room parallel to each other, as room the two sides. Due to the fact that this has two bag of parallel lines, and also a trapezoid must have actually *only one*, this is no a trapezoid. Sorry, buddy.

Like kites with their one-of-a-kind diagonals, trapezoids additionally have parts with special names (although none together strange as the name we have for our parts). A trapezoid has actually two bases, each of which is one of the parallel sides. The other two sides that aren"t parallel to each other are called the trapezoid"s legs.

Since just the bases room parallel and also the legs room not, we can think the this script as two nonparallel transversals cutting throughout a pair that parallel lines.

Looking at ∠1 and also ∠2, we deserve to see the they room consecutive interior angles. Very same goes for ∠3 and also ∠4. We already know (thanks come our considerable background in working with parallel lines) that consecutive internal angles room supplementary, so we"ve proven the consecutive angle in a trapezoid that share the very same leg room supplementary.

When both legs of the trapezoid room the same length, we have a special form of quadrilateral called an **isosceles trapezoid**.

As you can expect, isosceles trapezoids have congruent legs and also congruent consecutive angles shared by a base. The course, while isosceles triangle only have one "base" to job-related with, isosceles trapezoids have actually two. Twin the fun, we say.

### Sample Problem

If trapezoid *JANE* is isosceles and one of its base angles is 73° in measure, what space the measures of the various other three angles?

There are numerous different ways of figuring the end the steps of ∠1, ∠2, and also ∠3, however we"ll start off v the fact that in an isosceles trapezoid, both angle that re-publishing a base room congruent. Due to the fact that the 73° angle and ∠3 share base *JE*, they"re congruent. In various other words, m∠3 = 73°.

We likewise know that since ∠2 and also ∠3 room consecutive inner angles, they"re supplementary. We understand the measure up of ∠3, therefore let"s discover the measure up of ∠2.

m∠2 + m∠3 = 180°m∠2 + 73° = 180°m∠2 = 180° – 73°m∠2 = 107°

What about ∠1? due to the fact that it shares a base v ∠2, these two angles are congruent to every other. That way m∠1 = 107° together well.

We can double check this by remembering the all quadrilaterals have actually interior angle that add up come 360°. If we take the sum of these four angles, that"s the number we have to get.

73° + 73° + 107° + 107° ≟ 360°360° = 360°

Yup. Those are the angle we"ve got. No doubt around it.

Every quadrilateral has actually its VIPs, or very Important Polygons. The already exclusive trapezoid club is no exception. The VIPs the the trapezoid household are the isosceles trapezoids. If castle aren"t glorified for their congruent basic angles and legs, then your diagonals execute the talking. Yes, that"s right: isosceles trapezoids have actually congruent diagonals. Don"t think us? We"ll give you a hint: it"s because of a small something called SAS. (No, not "sass.")

Another kind of VIP in the trapezoid realm is the **right trapezoid**, which has one right angle. Of course, where that best angle is, it"ll have one more consecutive to it due to the fact that the bases are parallel to each other.

Even though not all trapezoids are developed equal, we"ll require something come unify every trapezoids so they don"t have a civil war or something. Therefore we"ll give each trapezoid—even those regular old non-isosceles ones—this belt-like thing dubbed a median. It level the playing ar and likewise helps them suck in those guts after a hearty Thanksgiving meal.

The **median** the a trapezoid is a segment parallel to the bases the connects the midpoints of the non-parallel sides. This line is special due to the fact that we deserve to determine that length directly from the size of the two bases. No joke.

The size of the typical of a trapezoid, *L*, is one-half the amount of the lengths the the bases, *B*1 and *B*2.

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### Sample Problem

Quadrilateral *ABCD* is a trapezoid, and *EF* is the mean of the trapezoid. What is the length of *EF*?

Since we understand the lengths that the 2 bases, we have the right to use the mean formula to uncover this length.