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Primary 5 Maths: Properties of 4-sided Figures

The common 4-sided figures learnt in Primary 5 are parallelogram, rhombus, trapezium and isosceles trapezium. Master the properties/characteristics of these 4-sided figures!


(1) Parallelogram

AB parallel with DC. 

That's why we can say adjacent angles, angle a + angle d = 180 degree, similarly angle b + angle c = 180 degree.

DA parallel with CB. 

So adjacent angles, angle d + angle c = 180 degree, similarly angle a + angle b = 180 degree.

In addition, angle b = angle d (opposite angles), angle c = angle a.

(2) Rhombus

AB parallel with DC and DA parallel with CB. 

That's why rhombus has all the same properties as parallelogram above. 

In rhombus, all sides are equal , hence angle d1 = angle d2 = half of the angle d.

(3) Trapezium 

AB parallel with DC.

Therefore, adjacent angles, angle a + angle d = 180 degree, similarly angle b + angle c = 180 degree.

NOTE: (very important !)

adjacent angle d + angle c is NOT EQUAL to 180 degree

adjacent angle a + angle b is NOT EQUAL to 180 degree.

It is because AD is not parallel with BC.

(4) Isosceles Trapezium

AB parallel with DC.

AD = BC (isosceles), therefore the base angle d = angle c.

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