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.

# CA Geometry: Area, pythagorean theorem

26-30, area, circumference, pythagorean theorem. Created by Sal Khan.

## Want to join the conversation?

• Quadrilateral just means "four sides"
(quad means four, lateral means side).

Any four-sided shape is a Quadrilateral.
• how do you know when to use pythagorean theorem when the problem doesnt directly ask you to?
(1 vote)
• If you have a right triangle with two side lengths and the third side length missing, you know you have to use the Pythagorean Theorem to find the third side.
• 1. At , what does 'Lateral area of a cone' MEAN..??
(1 vote)
• I am not sure, but my best guess would be it's the surface area of a cone.
• where can i find an actual word problem that is a theorem he hasn't explained them yet and my mom said he did explain it please can someone help.
(1 vote)
• At why can't you just do 8 * 21?
(1 vote)
• It would be perfectly fine to do 8 * 21.
I'm sure you understand, but for the benefit of others who are reading this, I will explain the reasoning.

The kite ABCD can be divided into two congruent triangles, triangle ABC and triangle ACD. The sum of the areas of these two triangles is equal to the area of the kite. Since the two triangles are congruent, they have the same area. So that means we can just figure out the area of one triangle and then double it to get the area of the kite.
The base of triangle ABC is 6+15 and its height is 8. The area of the triangle is is half of base times height, so we get 1/2 * (6+15) * 8. But since we are doubling it, it will just cancel out the 1/2. Which leaves us with just (6+15) * 8 = 21 * 8 = 168.
• What was he doing at around ? I don't understand.
• He was writing an equation to solve the problem.
(1 vote)
• are the diagonals of an isoscels trapezoid congruent?
(1 vote)
• Yes, the diagonals of an isosceles trapezoid are congruent.
(1 vote)
• What is the lateral area of a cone? Is that just a fancy way of saying the area of the cone?
(1 vote)
• lateral area is basically the area of the whole thing except the bottom part so it is just what goes around the top part :)
(1 vote)
• Can you explain Lateral area please
(1 vote)
• the surface area of a 3D object such as prism, cylinder, cone etc
(1 vote)
• I don't understand what lateral area is...question 28 at about . Can anyone explain it to me (besides what the formula is b/c that's given)?
(1 vote)
• notice the shape, height, base, l is the hypotenuse of a pythagorean triangle. So a squared (base) + b squared (length) = c squared (L). So 5 squared is 25 and b squared is 64 add them it is 89.
(1 vote)