# Area of triangles: height intersects with the base outside the triangle

Learning Material  |  Interactive Lesson

Description
Find the area of triangles with vertical or horizontal sides. In this type of triangle, the base may be chosen so that the height intersects with the base outside the triangle. Explore how the formula for finding the area of a triangle works. First, estimate the area of a chosen triangle on a grid. Next, work out the correct formula by assembling a series of triangles and rectangles. Then, compare the actual area of the triangle with your original estimate. Practise applying the formula directly to a range of triangles. This learning object is one in a series of four objects.
Objective
1. Students estimate the area of triangles.
2. Students identify the base and height pairs of triangles, including those situations where the height intersects the base outside the triangle.
3. Students identify the relationship between area of triangles and rectangles.
4. Students establish that all three base-height pairs can be used to calculate the area of triangles.
5. Students identify and apply the correct formula for calculating the area of a triangle.

#### Curriculum Information

 Education Type K to 12 Grade Level Grade 7, Grade 8, Grade 9, Grade 6 Learning Area Mathematics Content/Topic Measurement Intended Users Educators, Learners, Students Competencies