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.

Buying the New Tudor Black Bay Chrono 'Pink'

Charlie Munger: Avoid These Mistakes and You Will Double Your Net Worth

View All

The Ponzi Factor - Short Trailer

When we think about the stock market, we think about money, the finance industry, businesses, and making money from investing in successful businesses. The belief is investing in successful businesses is what leads to investment profits, and there’s a dir…

Biology overview

[Voiceover] I would like to welcome you to Biology at Khan Academy. And biology, as you might know, is the study of life. And I can’t really imagine anything more interesting than the study of life. And when I say “life,” I’m not just talking about us, h…

Multiplying and dividing decimals by 10

We’ve already learned that when we multiply by ten, let’s say we took the number 53 and we were to multiply it by ten, it has the effect of shifting all the digits one place to the left. So this should be a review for you, but this was going to be 530. We…

He Risked Death as First American to Explore Africa's Deepest Parts | National Geographic

We have to go back to who William Stamps Cherry was at the age of 20. He does head out for Africa against everybody’s advice, who said, “You’re going to die over there.” He went into Africa in 1889 and went further in the Congo than any other white man ha…

PPCs for increasing, decreasing and constant opportunity cost | AP Macroeconomics | Khan Academy

So we have three different possible production possibilities curves for rabbits and berries here, which we’ve already talked about in other videos. But the reason why I’m showing you three different curves is because these three different curves clearly h…

Sleepy Cubs | America's National Parks

A black bear and her cubs – a typical litter of three. For 5 months, she hasn’t stirred. Even as their mother slumbered, the cubs nursed on a rich diet of super fatty milk. Over the winter, her own weight dropped up to 1⁄3. How she survived still stumps u…

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

More Articles