Main content

## 6th grade (Illustrative Mathematics)

### Unit 1: Lesson 5

Lesson 9: Formula for area of a triangle# Finding area of triangles

To find a triangle's area, use the formula area = 1/2 * base * height. Choose a side to use for the base, and find the height of the triangle from that base. Then, plug in the measurements you have for the base and height into the formula.

## Video transcript

- [Instructor] What is
the area of the triangle? And they're talking
about this triangle here. And like always, pause this video and see if you can figure
it out on your own. Alright, now let's work
through it together. So we know that the area of a triangle is going to be equal to one half times our base, times our height. Let me do the height in a different color. Times our height. So what is the length of
our base in this scenario? Well the base is this 18 right over here. Let me highlight it. This length right over here is our base. So the base is 18, and what is the height? Well the height we see is six. They give it to us. They don't always give it to you, but in this example they do. So the height is, the height, the height is, I'm having
trouble with my pen, is six, so now we just have to compute what one half times 18 times six is. Well let's think about this a little bit. One half times 18 is nine. Nine times six is equal to what? Nine times six is equal to 54. And we're done. This is 54 square units.