If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

### Course: Basic geometry and measurement>Unit 8

Lesson 4: Area of composite figures

# Area of quadrilateral with 2 parallel sides

Learn how to find the area of a quadrilateral by splitting it into two triangles. Use the formula for triangle area (1/2 base times height) for each triangle. Add the areas together for the total quadrilateral area. It's as easy as pie...or should I say, as easy as area! Created by Sal Khan.

## Want to join the conversation?

• it would have been much faster is he just did 8*5=40/2 which equals 20 and then 4*5=20/2 whish is 10 then add them which is 30
• as he said, you could just evaluate it. nut he also introduced a couple of interesting concepts instead. any problem has multiple solutions, the one shown here brings us closer to understanding deeper truths about math and stuff
(1 vote)
• why the height for second triangle is 5 :/
• The height is perpendicular to the base, so you would have to extend the line segment of the base which is 4 at least to the point of vertex on top left. Then the same 5 on bottom would be the perpendicular distance to this vertex. Think of the two bases as being parallel, distance between them will remain constant.
• It will be much easier and quick if you make a parallelogram and a triangle out of the shape first and then it is just 20 + 10 = 30 unit
• Me: Accidentally clicks on someone elses boi
Also me: "NOOOOOOOOOOO😭" *Video restarts🥲*
• Isn't a quadrilateral with 2 parallel sides just another parallelogram?
• Shouldn't you be doing this for a trapezium? (We call that in Hong Kong):
(8+4)x5/2
=12x5/2
=60/2
=30
• well some people only learned the area of the triangle so you just split it up into 2 triangles
• Is there a shortcut for this?
• 4x5=20 20/2=10
8x5=40 40/2=20

20 + 10 = 30
A = 30
• It's too confusing and I keep getting the questions wrong.
• how do i do area of composite shapes