--- title: "Properties of rectangles" description: "Use the properties of rectangles to deduce related facts and find missing lengths and angles" canonical: https://lightmysky.com/learn/mathematics/properties-of-rectangles-mt_KFKUR_gBg_ source: https://lightmysky.com/learn/mathematics/properties-of-rectangles-mt_KFKUR_gBg_.md retrieved: 2026-09-02 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Properties of rectangles Use the properties of rectangles to deduce related facts and find missing lengths and angles Subject: Mathematics · Area: Geometry · Ages 9 to 10 Page: https://lightmysky.com/learn/mathematics/properties-of-rectangles-mt_KFKUR_gBg_ ## Ready when they can - 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 ## Lesson: Rectangle sides 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°. *(drawing: Opposite sides are equal in length, and every corner is a 90° angle.)* **Example.** 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. **Tip.** 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. **Example.** 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. **Recap.** A rectangle's opposite sides are equal, every corner is 90°, and you can find a missing side using the perimeter or the area. ## Practice 20 questions on this page, each with its working shown. ## Needs first - [Area and perimeter of rectangles](https://lightmysky.com/learn/mathematics/area-and-perimeter-of-rectangles-mt_eiB3-6pu6a) - [Classifying quadrilaterals](https://lightmysky.com/learn/mathematics/classifying-quadrilaterals-mt_Xt1cRqaBOW) ## Opens up - [Understanding angles (age 10+)](https://lightmysky.com/learn/mathematics/understanding-angles-age-10-mt_QDTO3GAgcq)