Understanding angles (age 9+)

Use the properties of rectangles to deduce related facts and find missing lengths and angles

ages 9 to 108 practice questionsvideo included

What a learner can do afterwards

Given one side of a rectangle is 8 cm and the perimeter is 28 cm, find the other side
Explain that all angles in a rectangle are 90°
Find a missing side of a rectangle given its area and one side length

The lesson

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°.

Opposite sides are equal in length, and every corner is a 90° angle.

Try it together

A garden is shaped like a rectangle. One side is 8 cm long, and going all the way around measures 28 cm. Half of 28 is 14, so the two different side lengths add up to 14. Since one side is 8, the other side is 14 - 8 = 6 cm.

Good to know

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.

Tap to fill the grid, one at a time: 4 rows of 6.

This grid shows how area works: count the rows and columns, then multiply to find the total squares inside a rectangle.

A rectangle's opposite sides are equal, every corner is 90°, and you can find a missing side using the perimeter or the area.

Watch it

Where it sits

Learn first

Estimating answers (age 9+)Understanding angles (age 8+)

This opens up

Nothing builds on it yet.

Where this leads

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

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Then practise

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.