Use the properties of rectangles to deduce related facts and find missing lengths and angles
A rectangle has four straight sides and four corners. The two sides across from each other are always the same length. Every corner makes a right angle, which measures 90°.
A garden bed is drawn as a rectangle. One side is 7 cm, and the perimeter, the distance all the way round, is 24 cm. Opposite sides match, so half of 24 is one long side plus one short side: 12 cm. One of those two is the 7 cm side, so the other is 12 - 7 = 5 cm.
All four angles in a rectangle are always 90°, no matter how long or short the sides are. You never need to measure them to know that.
Area asks a different question: how much space is inside. Cover the same bed with 1 cm squares. It is 7 squares across and 5 squares down, so 7 × 5 = 35 square cm. That works backwards too. If you know the area and one side, divide to get the other side.
A rectangle's opposite sides are equal, every corner is 90°, and you can find a missing side using the perimeter or the area.
You have been sorting shapes by their corners, hunting for the square mark that means a right angle. Mia's plan for the new play area has a flower bed on it: a rectangle with one side 7 cm, and 24 cm of string all the way round.
Zara reaches for a ruler to measure the other three sides. What does the 7 cm side already tell you, before anybody measures anything?
This opens up
Nothing builds on it yet.
Jobs that lean on this skill. Follow one to see everything it is built on.
20 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.