Year 3 Parallel and perpendicular sides in polygons worksheet

“Shapes from two triangles” is free to print, with no account. It is the first sheet in the Year 3 maths unit “Parallel and perpendicular sides in polygons”, for children aged 7 to 8, and takes about 20 minutes.

Print it on A4. The child's pages come first; the answers, and what each wrong answer tells you, are on the grown-up page that follows. Weeks 33 to 35 of the year, 10 sheets in the unit.

Free sample · answers on the last page

Shapes from two triangles

Name: ____________ · Date: ____________
Year 3 · Maths · about 20 minutes
Answers are on the grown-up page

Today I can name the new shape made when two identical triangles are joined in different ways.

A Look back3 min

1.
A pentagon has sides.
2.
Each side of this square is 3 cm. The perimeter is cm.
3.
A rectangle has corners.

B Watch me, then you4 min

Two identical right-angled triangles sit on a table. Ola turns one and joins it to the other.

Watch me

Turn one triangle half a turn.

Slide it so the longest sides meet exactly.

Draw round the outside. The join line goes, leaving a rectangle.

Now you

1.
Join two identical triangles along a short side with a half turn. Circle the new shape.
triangleparallelogrampentagon

C Your turn5 min

Every row uses the same two identical right-angled triangles. Read each join carefully before you answer.

1.
Join the longest sides with a half turn. The new shape has sides.
2.
Join a short side with a half turn. The new shape has sides.
3.
Join a short side, but flip one triangle over instead of turning it. The new shape has sides.
4.
Join the longest sides, but flip one triangle over. The new shape has sides.

Say it out loud: Which change made a triangle again, and which change made four sides? Why?

D Spot the mistake3 min

Ola says: “Two triangles can only ever make another triangle, because they are both triangles.”

1.
Two identical right-angled triangles are joined along their longest sides after one is given a half turn. Circle the new shape.
trianglerectanglepentagon

E Think deeper4 min

Join two identical triangles in any way you choose. Try a join that does not make a rectangle.

1.
Draw the new shape and name it. Does it have a pair of parallel sides? Say how you know.

How did it feel?

I can do it Nearly Not yet

For the grown-up

Shapes from two triangles · 2 minutes to read

Answers, and what a wrong one tells you

A

1. 5

2. 12 your child may have added only three sides, 3+3+3=9. A square has four sides, so add the fourth 3 as well to get 12.

3. 4

B

1. parallelogram your child may still see the two small triangles. Ask them to draw round the outside of both pieces together, so the join line disappears, then count the sides and check for two pairs of parallel sides.

C

1. 4

2. 4

3. 3 your child may have counted all the sides of both triangles, 3+3=6. Only the outside edges count, so trace round the outline only.

4. 4

D

1. rectangle your child may still think the pieces make a triangle. Draw round the outside of both pieces together, and look at the outline, not the two small shapes.

E

1. Look for: A drawn shape with a name such as parallelogram, kite or triangle, and a reason about whether a pair of sides stays the same distance apart.

Words to use

Say“Draw round the outside. Where did the inside join line go?”

Instead of“Tell them the shape is a rectangle before they have drawn round it.”

After the sheet

Cut two identical triangles from paper, join them in two ways, draw round the outside, and name each shape.

Tick what your child got right in StudyDen. Anything missed comes back in a later Look back box, so there's no need to redo the sheet.

The rest of this unit

9 more sheets come with a StudyDen plan, in teaching order:

Cutting up polygons(with a plan)
Checking every pair of sides(with a plan)
Parallel sides in shapes(with a plan)
Joined shapes and their corners(with a plan)
Parallel sides spotted(with a plan)
Triangles on a Circle(with a plan)
Naming quadrilaterals(with a plan)
Shapes to order(with a plan)
Drawing shapes with properties(with a plan)

Every Year 3 maths worksheet

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