Area of a Triangle
(KS3, Year 7)
The LessonThe area of a triangle is found using the formula:
In this formula, b is the length of the base of the triangle and h is the height of the triangle. The image below shows what we mean by the lengths of the bases and the height:
How to Find the Area of a TriangleFinding the area of a triangle is easy.
QuestionWhat is the area of a triangle with a base of 5 cm and a height of 3 cm, as shown below?
Start with the formula:
Area = ½bhDon't forget: ½bh = ½ × b × h
Substitute the length of the base and the height into the formula. In our example, b = 5 and h = 3.
Area = ½ × 5 × 3 = 7.5 cm2Don't forget: ½ × a number = 0.5 × a number = a number ÷ 2.
Answer:The area of the triangle with a base of 5 cm and a height of 3 cm is 7.5 cm2.
"Find the Area" Widget
- Click on the shape you're learning about.
- Click on the pad to start.
- Follow the instructions in the bottom-left corner.
- On the last click, the formula, workings, and answer will appear in the yellow box.
- Good luck!
Lesson SlidesThe slider below shows another real example of how to find the area of a triangle. Open the slider in a new tab
How to Find the Area of a Triangle Using TrigonometryThe area of a triangle can also be found using trigonometry. The area is found using the formula:
In the formula, a and b are lengths of two sides of the triangle and C is the angle between them. The image below shows what we mean by the two sides and the angle between them:
Read more about how to find the area of a triangle using trigonometry
What Is a Triangle?A triangle is a flat shape with three straight sides and three corners (also called vertices). There are different types of triangle:
What's in a Name?A triangle has three corners and so three angles. Just as a tricycle has three wheels, and a tripod has three legs, a shape with three angles in called a triangle.
Areas of Triangles and RectanglesThe area of a triangle is ½bh. The area of a rectangle is bh. The area of the triangle is half that of the rectangle with the same base length and height. Can you see from the image of a right-angled triangle below that this is the case?
What about this triangle below?
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