## Trapezoids

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

While the rest of them have their congruent sides and angles to chitchat about, this quadrilaterals simply hang by the snack bar. Every when in a while, they can strike increase a conversation v a lonesome polygon who happens come wander over, but it never lasts long and they just go earlier to uncomfortably staring at their feet.

A **trapezoid** is a quadrilateral through *only one* set of parallel sides. Lock absolutely *cannot* have two sets of parallel sides. So as soon as trapezoids start their very own party after gift kicked out of the square party, we deserve to be particular that rectangles, squares, and parallelograms will definitely not it is in on the guest list. Take it that, suckers.

### Sample Problem

Is this square a trapezoid?

How plenty of pairs of parallel lines perform you see? The top and also bottom room parallel to each other, as are the two sides. Because this has two pairs of parallel lines, and also a trapezoid must have *only one*, this is not a trapezoid. Sorry, buddy.

Like kites v their distinct diagonals, trapezoids additionally have components with special names (although none together strange together the surname we have for our parts). A trapezoid has actually two bases, each of which is among the parallel sides. The other two sides the aren"t parallel come each other are referred to as the trapezoid"s legs.

Since just the bases are parallel and the legs room not, we have the right to think the this script as 2 nonparallel transversals cutting throughout a pair of parallel lines.

Looking at ∠1 and ∠2, we deserve to see that they space consecutive interior angles. Very same goes because that ∠3 and ∠4. We already know (thanks to our substantial background in working through parallel lines) the consecutive internal angles room supplementary, therefore we"ve proven that consecutive angles in a trapezoid that share the exact same leg room supplementary.

When both foot of the trapezoid are the same length, we have actually a special form of quadrilateral dubbed an **isosceles trapezoid**.

As you could expect, isosceles trapezoids have congruent legs and congruent consecutive angles common by a base. Of course, while isosceles triangle only have one "base" to work-related with, isosceles trapezoids have actually two. Double the fun, us say.

### Sample Problem

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

There are plenty of different methods of figuring the end the measures of ∠1, ∠2, and ∠3, however we"ll start off with the reality that in one isosceles trapezoid, both angles that re-publishing a base room congruent. Because the 73° angle and ∠3 share basic *JE*, they"re congruent. In various other words, m∠3 = 73°.

We additionally know that due to the fact that ∠2 and also ∠3 room consecutive interior angles, they"re supplementary. We know the measure up of ∠3, so let"s uncover the measure up of ∠2.

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

What around ∠1? since it shares a base v ∠2, these two angles room congruent to each other. That method m∠1 = 107° together well.

We can twin check this by remembering that all quadrilaterals have actually interior angles that add up come 360°. If us take the sum of these 4 angles, that"s the number we must get.

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

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

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

Another type of VIP in the trapezoid kingdom is the **right trapezoid**, which has one best angle. Of course, where that ideal angle is, it"ll have an additional consecutive come it due to the fact that the bases room parallel to each other.

Even though not all trapezoids are developed equal, we"ll need something come unify every trapezoids therefore they don"t have a civil war or something. For this reason we"ll provide each trapezoid—even those consistent old non-isosceles ones—this belt-like thing referred to as a median. It level the playing ar and additionally helps castle suck in those guts after a hearty Thanksgiving meal.

The **median** the a trapezoid is a segment parallel to the bases that connects the midpoints that the non-parallel sides. This heat is special because we have the right to determine that is length directly from the length of the two bases. No joke.

The length of the mean of a trapezoid, *L*, is one-half the sum of the lengths the the bases, *B*1 and also *B*2.

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### Sample Problem

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

Since we understand the lengths that the 2 bases, we can use the mean formula to discover this length.