Idea 11of 22Builds onA parallelogram becomes a rectangle
The height goes straight up
Which length do you multiply the base by?
Today you'll discover
- why the slanted side is too long
- how to spot the height
- what a flatter lean does
Think firstBase 8 cm, slanted sides 5 cm
Is the area of this parallelogram 8 × 5 = 40 cm²?
Decide first, then press Next. Find the line that meets the base at a square corner.
A low parallelogram, base 8 cm, slanted sides 5 cm. A dashed blue height drops straight to the base with a small square at the bottom: 3 cm. The left triangle slides to the right to make an 8 by 3 rectangle, and the line 8 × 3 = 24 cm² appears. The last step shows the parallelogram with base 6 cm, height 4 cm and slanted sides 5 cm.
See the whole ideathe big idea and the key word, in one place
The big idea
The height is the distance straight up from the base, perpendicular to it, never the slanted side.
Compare themSlanted side: leans, 5 cm long. Height: straight up, 3 cm. Only the height and the base give the area.
Easy to get wrongA flatter lean keeps the slanted side 5 cm long but makes the height shorter, and the area smaller.
Key words
- height
- the distance straight up from the base to the opposite side or corner
- perpendicular
- meeting at a square corner, a right angle
Ready to use it?
- Pick the height, not the slanted side, to find a parallelogram's area.