A triangle is just half of a rectangle, to find the area of a triangle, you find the area of the rectangle the triangle fits inside and divide it by 2. Here are some vocabulary words to help with the lesson.

**Base**: The width of a triangle**Perpendicular**: 2 lines that touch at a 90 degree angle. (See the information box on right angles within the lesson on the perimeter of a rectangle.)**Adjacent sides**: Sides of a shape that meet at a corner

Area of a Triangle

Video Source (05:49 mins) | Transcript

\(\displaystyle \text{Area of Triangle} = \frac{1}{2}\text{base} \times \text{height} = \frac{1}{2}{\text{bh}}\)

Remember that the base and the height have to be perpendicular to each other. In this course, we will provide the base and height values.

## Additional Resources

- Khan Academy: Area of a Triangle (5:29 mins | Transcript)

### Practice Problems

- A triangle has a base of 10 mm and a height of 12 mm. Use the formula for the area of a triangle to determine the area of this triangle. (Solution
- A triangle has a base of 5 inches and a height of 7 inches. Use the formula for the area of a triangle to determine the area of this triangle. Round to the nearest tenth. (Solution
- A right triangle has perpendicular adjacent sides of lengths 21 cm and 25 cm. Use the formula for the area of a triangle to calculate the area of this triangle. Round to the nearest tenth. (Solution
- The top of a slice of blueberry pie is in the shape of a triangle. The slice is 4 inches wide at the widest point and is 7 inches long. Use the formula for the area of a triangle to determine the surface area of the top of this slice of blueberry pie. (Video Solution
- A garden that is in the shape of a triangle has a width of 35 ft and a length of 55 ft. Use the formula for the area of a triangle to determine the area of this garden. Round to the nearest whole number. (Solution
- A large triangular window has a base of 3 m and a height of 4 m. Use the formula for the area of a triangle to calculate the area of this window. (Video Solution

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