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Class 8

Chapter 4: Quadrilaterals

A quadrilateral has 4 sides. The 4 interior angles always sum to 360°. Common kinds include square, rectangle, rhombus, parallelogram and trapezium.

Learning outcomes

  • Classify quadrilaterals by properties
  • Apply angle-sum and side properties

Activities

  • Construct & classify with paper folds

Worked examples

Read through these first, then try the practice below.

  1. Example 1 — Find the missing angle

    Three angles of a quadrilateral are 90°, 100° and 80°. What is the fourth?

    Solution: 360 − (90 + 100 + 80) = 90°.

  2. Example 2 — Classify it

    A quadrilateral has both pairs of opposite sides parallel and all angles 90°. What is it?

    Solution: A rectangle.

Self-do practice

Question 1 of 3 · Score 0/0

Three angles of a quadrilateral are 70°, 110° and 60°. What is the fourth?

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