Writing equations to represent geometric problems | Grade 8 (TX TEKS) | Khan Academy

less than 1m read

·Nov 10, 2024

We're told the perimeter of the rectangle shown is 17x units. The area of the rectangle is 15x square units. Write an equation that represents the perimeter, and also write an equation that represents the area.

So pause this video and see if you can write those two equations.

All right, now let's do this together. So let's tackle this first one. Write an equation that represents the perimeter. The perimeter is going to be the length of all of the sides. So you have this side right over here which is 4x + 2, and then you're going to add this side over here, which is 2 and a half, plus this side over here which is going to be 4x + 2 again. So, plus 4x + 2, plus this side which is going to be 2 and A2 plus 2 and a half. Well, that's going to be equal to the perimeter, which they told us is 17x units. So that is going to be equal to 17x.

And we're done! That's all they wanted; they just want us to write an equation that represents the perimeter. We don't have to solve it.

So now let's do the same thing for the area. The area of a rectangle is going to be our base times our height, or our height times our base. So we could say it's 2 and A2 * (4x + 2). Then, that's going to be our area, which they say is 15x² units. So that's equal to 15x. We could have also written it the other way; we could have said that the area, which is 15x, is equal to 2 and A2, the height, times (4x + 2).

So, a lot of different ways to approach it, but in both cases, we are now done.

He Builds Space Robots for a Living | Best Job Ever

Know Why You're Starting a Company - Danae Ringelmann of Indiegogo

View All

Will OpenAI Kill All Startups?

This is Michael Seibel with Dalton Caldwell, and today we’re going to talk about how OpenAI is going to kill all startups. This is our last video; might as well pack it in, we’re done. OpenAI is going to do this. They’re going to make the videos—next vide…

Help Khan Academy this holiday season

Hi everyone, Sal Khan here from Khan Academy, and I just want to first of all express my gratitude to all of you who have supported Khan Academy over the years. I also wanted to reach out to those of y’all who haven’t, because as you know, we are not-for…

The Battle Between Eel and Stonefish Is One-Sided | National Geographic

Today in the ocean, a life-or-death battle between two extremely capable predators. First up is the stonefish, the killer who hides in plain sight, with sharp spines containing enough venom to kill a person. We’ve chosen a shot of it missing its prey. I’…

Worked example: Rewriting expressions by completing the square | High School Math | Khan Academy

Let’s see if we can take this quadratic expression here, ( x^2 + 16x + 9 ), and write it in this form. You might be saying, “Hey Sal, why do I even need to worry about this?” One, it is just good algebraic practice to be able to manipulate things. But as…

London dispersion forces introduction | States of matter | High school chemistry | Khan Academy

What we’re going to do in this video is start talking about forces that exist between even neutral atoms or neutral molecules. The first of these intermolecular forces we will talk about are London dispersion forces. So, it sounds very fancy, but it’s act…

Scaling Growth | Gustaf Alstromer, YC Partner (formerly Airbnb) & Ed Baker (formerly Uber)

What’s pretty cool is a few guys who have been living the centre of building up these growth teams kind of for the past, you know, seven or eight years. Edie joined Uber to start the growth team when it was five people, and then over the three and half ye…

Writing equations to represent geometric problems | Grade 8 (TX TEKS) | Khan Academy

More Articles