Define the term congruent .

Two shapes are congruent if they are identical in shape and size .

True or False? If one shape is an enlargement of the other, then they are congruent .

False. If one shape is an enlargement of the other, then they are not identical in size and so are not congruent .

True or False? You need to show that two shapes are facing in the same direction to prove congruence .

False. If the two shapes are identical in terms of shape and size then it does not matter which direction they are facing in.

Define the term similar shapes .

Two shapes are similar if they have the same shape and their corresponding sides are in proportion . One shape is an enlargement of the other.

True or False? If two triangles of different sizes have the same angles they are not similar .

False. If two triangles of different sizes have the same angles they are similar . One is an enlargement of the other.

True or False? Shapes that are not triangles can have the same angles and not be similar .

True. Some shapes that are not triangles can have the same angles and not be similar . E.g. two rectangles of different sizes will have the same angles but their corresponding sides could have different scale factors.

True or False? To show that two non-triangular shapes are similar you need to show that their corresponding sides are in proportion .

True. To show that two non-triangular shapes are similar you need to show that their corresponding sides are in proportion .

What is a scale factor , in the context of similarity?

A scale factor is the ratio of corresponding lengths in similar shapes .

True or False? In the context of similarity, a scale factor cannot be negative .

True. Although you can have a negative scale factor in general enlargement, in the context of similarity , a scale factor cannot be negative .

What does a scale factor that is greater than 0 but less than 1 imply?

A scale factor that is greater than 0 but less than 1 implies that the similar shape is smaller than the original shape.

How can you find a length scale factor ?

A length scale factor can be found by dividing the length of a side on one shape by the length of a corresponding side on the similar shape.

Define a geometrical proof .

A geometrical proof uses known geometry rules to establish a new geometrical statement. Questions asking for one usually begin Prove or Show that .

What two things must every step of a geometrical proof contain?

Each step needs a fact and the reason that justifies it. Stating angle ABC = 40° is only half a step, because it must be paired with the rule it follows from, such as base angles of an isosceles triangle are equal .

True or False? Marking the angles onto the diagram is enough to show your working.

False. Annotating the diagram is a useful way to keep track, but the facts and reasons must also appear in your written answer . Work shown only on a diagram leaves the proof itself unwritten.

How should the reasons in a proof be written?

As short standard phrases rather than full sentences. Each one is the recognised name of a rule, such as angles on a straight line add up to 180° or corresponding angles are equal .

IGCSEMathsEdexcelMaths AFoundationFlashcards4. Geometry & TrigonometryCongruence, Similarity & Geometrical Proof

Congruence, Similarity & Geometrical Proof (Edexcel IGCSE Maths A: Foundation): Flashcards

Exam code: 4MA1

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Define the term congruent.

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Cards in this collection (17)

Define the term congruent.
Two shapes are congruent if they are identical in shape and size.
True or False?
If one shape is an enlargement of the other, then they are congruent.
False.
If one shape is an enlargement of the other, then they are not identical in size and so are not congruent.
True or False?
You need to show that two shapes are facing in the same direction to prove congruence.
False.
If the two shapes are identical in terms of shape and size then it does not matter which direction they are facing in.
Define the term similar shapes.
Two shapes are similar if they have the same shape and their corresponding sides are in proportion.
One shape is an enlargement of the other.
True or False?
If two triangles of different sizes have the same angles they are not similar.
False.
If two triangles of different sizes have the same angles they are similar.
One is an enlargement of the other.
True or False?
Shapes that are not triangles can have the same angles and not be similar.
True.
Some shapes that are not triangles can have the same angles and not be similar.
E.g. two rectangles of different sizes will have the same angles but their corresponding sides could have different scale factors.
True or False?
To show that two non-triangular shapes are similar you need to show that their corresponding sides are in proportion.
True.
To show that two non-triangular shapes are similar you need to show that their corresponding sides are in proportion.
What is a scale factor, in the context of similarity?
A scale factor is the ratio of corresponding lengths in similar shapes.
True or False?
In the context of similarity, a scale factor cannot be negative.
True.
Although you can have a negative scale factor in general enlargement, in the context of similarity, a scale factor cannot be negative.
What does a scale factor that is greater than 0 but less than 1 imply?
A scale factor that is greater than 0 but less than 1 implies that the similar shape is smaller than the original shape.
How can you find a length scale factor?
A length scale factor can be found by dividing the length of a side on one shape by the length of a corresponding side on the similar shape.
Define a geometrical proof.
A geometrical proof uses known geometry rules to establish a new geometrical statement.
Questions asking for one usually begin Prove or Show that.
What two things must every step of a geometrical proof contain?
Each step needs a fact and the reason that justifies it.
Stating angle ABC = 40° is only half a step, because it must be paired with the rule it follows from, such as base angles of an isosceles triangle are equal.
True or False?
In the notation angle $A B C$ , the angle is the one at $B$ .
True.
The middle letter always names the vertex where the angle sits.
So angle $A B C$ is the angle between the lines $A B$ and $B C$ .
How can you prove that the exterior angle of a triangle equals the sum of the two opposite interior angles?
Use the two different angle sums that each total 180°.
With interior angles $a$ , $b$ and $c$ , and $d$ the exterior angle beside $c$ , the triangle gives $a + b + c = 180$ while the straight line gives $c + d = 180$ .
Both totals are equal, so $a + b + c = c + d$ , and subtracting $c$ leaves $a + b = d$ .
True or False?
Marking the angles onto the diagram is enough to show your working.
False.
Annotating the diagram is a useful way to keep track, but the facts and reasons must also appear in your written answer.
Work shown only on a diagram leaves the proof itself unwritten.
How should the reasons in a proof be written?
As short standard phrases rather than full sentences.
Each one is the recognised name of a rule, such as angles on a straight line add up to 180° or corresponding angles are equal.

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