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?
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Jobs that lean on this skill. Follow one to see everything it is built on.
8 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.