Idea 13of 22Builds onTwo triangles make a parallelogram
A triangle's height can land outside it
Where is the height of a triangle that leans far over?
Today you'll discover
- how to extend the base
- where the height drops
- why the rule still works
Think firstA triangle whose top corner leans past its base
The top corner leans out past the base. Where is the height measured?
Decide first, then press Next. Follow the base line past the end of the triangle.
A triangle with base 4 cm whose top corner sits to the right of the base. An orange dashed line extends the base to the right, and a blue dashed height drops 5 cm straight down to it, outside the triangle, with a square corner mark. A blue copy turns into place to make a parallelogram, 4 × 5 = 20 cm², and the triangle is half: 10 cm². The last step shows a triangle leaning out to the left.
See the whole ideathe big idea and the key word, in one place
The big idea
The height runs from the top vertex straight to the base line, even outside the triangle.
Compare themPointed triangle: the height falls inside it. Leaning triangle: the height falls outside, on the base line made longer. The rule is the same.
Easy to get wrongExtend the base with a dashed line, but measure the base itself: 4 cm, not the dashed part too.
Key word
- vertex
- a corner of a shape, where two sides meet
Ready to use it?
- Find the height and area of a triangle that leans past its base.