Quadrilaterals
Properties of the square, rectangle, parallelogram, rhombus and trapezium, and finding unknown angles in them.
⏱ 6 min · 🎯 4 things to master
A is any four-sided shape — and the PSLE expects you to tell five special ones apart by their sides and angles. This is a P5 topic. The good news is that each shape has a short list of properties, and one shared rule about their angles, that together answer almost every question. Learn the lists and the rule, and these become reliable marks.
Parents: ask your child to name the shape and the property they will use before they reveal. The "Method tip" boxes name the exact property a PSLE marker rewards.
By the end you'll be able to name each quadrilateral by its properties, use parallel and equal sides, and find unknown angles. Let's sort them out.
Square and rectangle
A has four equal sides and four right angles. A has opposite sides equal and four right angles. Both have four 90-degree corners, which is why corners of tables and screens are these shapes.
The key difference is the sides: a square's four sides are all equal, while a rectangle only needs its opposite sides equal. Every square is a special rectangle, but not every rectangle is a square.
🤔 Predict first: Which shape has four equal sides AND four right angles?
Parallelogram and rhombus
A has two pairs of parallel sides, with opposite sides equal and opposite angles equal. A is a parallelogram with all four sides equal — like a pushed-over square.
In both shapes, opposite angles are equal and two angles that sit next to each other along a side add up to 180 degrees. These two facts solve most parallelogram angle questions.
🤔 Predict first: In a parallelogram, one angle is 70 degrees. What is the angle OPPOSITE to it?
Trapezium
A has just one pair of parallel sides. The other two sides are not parallel. This single pair of parallel lines is what tells a trapezium apart from a parallelogram.
In a trapezium, the two angles on the same slanted side (between the two parallel lines) add up to 180 degrees, because they are angles between parallel lines. That fact lets you find a missing angle from its partner on the same side.
🤔 Predict first: How many pairs of parallel sides does a trapezium have?
The angle sum is 360 degrees
Every quadrilateral shares one rule: the four angles add up to 360 degrees. So if you know three angles, subtract them all from 360 to find the fourth.
For example, a quadrilateral has angles 90 degrees, 90 degrees, 100 degrees and x. Then x = 360 − 90 − 90 − 100 = 80 degrees. This works for every four-sided shape, special or not.
🤔 Predict first: A quadrilateral has angles 80 degrees, 100 degrees, 90 degrees and x. What is x?
Watch out — these are easily mixed up
Quick recap
🎯 Mastery check
Answer all 6 — your progress is saved on this device.
Which shape has four right angles but does NOT need all four sides equal?
How many pairs of parallel sides does a parallelogram have?
In a parallelogram, one angle is 110 degrees. What is the angle opposite to it?
A quadrilateral has angles 70 degrees, 110 degrees, 80 degrees and x. What is x?
Which shape has exactly ONE pair of parallel sides?
In a parallelogram, one angle is 65 degrees. What is the angle right next to it along a side?