Primary 5 Parallelogram, Rhombus and Trapezium
Keywords
- Parallel
- Lines that stay the same distance apart and never meet.
- Opposite
- Across the shape, not beside each other.
- Adjacent
- Next to each other, sharing a side.
Parallelogram
A parallelogram has two pairs of parallel opposite sides.
Read the marks
Green arrows mark parallel sides.
- AB ∥ DC and AD ∥ BC.
- Opposite sides are equal: AB = DC and AD = BC.
- Opposite angles are equal. Adjacent angles add up to 180°.
Find the unknown angle
Angle A is 70°. What is angle x at B?
Reveal the answer
A and B are adjacent angles in a parallelogram, so they add up to 180°.
x = 180° − 70° = 110°.
Try together
One angle of a parallelogram is 65°. Find an adjacent angle.
Reveal the answer
180° − 65° = 115°.
Rhombus
A rhombus is a parallelogram with four equal sides.
Read the marks
Green arrows mark parallel sides.
- Both pairs of opposite sides are parallel.
- All four sides are equal.
- Opposite angles are equal. Adjacent angles add up to 180°.
Find the unknown angle
Angle H is 70°. What is angle x at F?
Reveal the answer
H and F are opposite angles in a rhombus, so they are equal.
x = 70°.
Try together
One angle of a rhombus is 48°. Find its opposite angle.
Reveal the answer
The opposite angle is 48°.
Trapezium
A trapezium has at least one pair of parallel opposite sides. Here, PQ ∥ SR.
Read the marks
Green arrows mark the parallel sides PQ and SR.
- PQ ∥ SR. The other two sides have no parallel marks.
- The two inside angles along side PS add up to 180°.
Find the unknown angle
Angle P is 60°. What is angle x at S?
Reveal the answer
PQ ∥ SR, so the angles along side PS add up to 180°.
x = 180° − 60° = 120°.
Try together
A lower angle of a trapezium is 75°. Find the upper angle on the same slanted side.
Reveal the answer
180° − 75° = 105°.