Trapezoid Area Calculation: Finding the Area of ABCD with Bases 5 and 11

Q: How do I identify which sides are the bases?

The bases are the two parallel sides of the trapezoid. In this problem, AB (length 5) and DC (length 11) are parallel to each other, so these are your bases.

Q: What if I can't see the height clearly?

The height is the perpendicular distance between the two parallel bases. Look for a dashed line or right angle symbol. In this diagram, the height appears to be the vertical line from A to the bottom base.

Q: Why do we multiply by 1/2 in the trapezoid formula?

Think of a trapezoid as the average of the two bases times the height. $ \frac{1}{2}(b_1 + b_2) $ gives you the average length, then multiply by height for the area!

Q: Can I use this formula for any quadrilateral?

No! This formula only works for trapezoids because they have exactly one pair of parallel sides. Rectangles, squares, and parallelograms need different formulas.

Q: What if my answer doesn't match any of the choices?

Double-check that you've identified the correct bases and height. Make sure you're adding the bases first, then multiplying by half the height. Common errors include using the wrong measurements.

Trapezoid Area with Given Base Lengths

Look at the following trapezoid:

Calculate the area of trapezoid ABCD.

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:03 First, let's calculate the area of the trapezoid.

00:07 Remember, we use the formula: Area equals the sum of the bases, A B plus D C, times the height, H, and then divide by 2.

00:15 Now, let's plug in the values and solve to find the area.

00:20 Next, divide 16 by 4 to continue solving the problem.

00:34 Finally, this is how we find the area of the trapezoid!

Step-by-step written solution

Follow each step carefully to understand the complete solution

Understand the problem

Look at the following trapezoid:

Calculate the area of trapezoid ABCD.

Final Answer

Key Points to Remember

Essential concepts to master this topic

Formula: Area = $\frac{1}{2}(b_1 + b_2) \times h$ where bases are parallel sides
Technique: Add bases first: 5 + 11 = 16, then multiply by half the height
Check: Verify height measurement is perpendicular to both parallel bases ✓

Common Mistakes

Avoid these frequent errors

Using the wrong sides as bases
Don't use the slanted sides (AD or BC) as bases = wrong calculation! These are the legs, not the parallel sides. Always identify the two parallel sides (AB = 5 and DC = 11) as your bases first.

Practice Quiz

Test your knowledge with interactive questions

Given the following trapezoid:

Calculate the area of the trapezoid ABCD.

FAQ

Everything you need to know about this question

How do I identify which sides are the bases?

The bases are the two parallel sides of the trapezoid. In this problem, AB (length 5) and DC (length 11) are parallel to each other, so these are your bases.

What if I can't see the height clearly?

The height is the perpendicular distance between the two parallel bases. Look for a dashed line or right angle symbol. In this diagram, the height appears to be the vertical line from A to the bottom base.

Why do we multiply by 1/2 in the trapezoid formula?

Think of a trapezoid as the average of the two bases times the height. $\frac{1}{2}(b_1 + b_2)$ gives you the average length, then multiply by height for the area!

Can I use this formula for any quadrilateral?

No! This formula only works for trapezoids because they have exactly one pair of parallel sides. Rectangles, squares, and parallelograms need different formulas.

What if my answer doesn't match any of the choices?

Double-check that you've identified the correct bases and height. Make sure you're adding the bases first, then multiplying by half the height. Common errors include using the wrong measurements.

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