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Congruent vs. Similar — What's the Difference?

By Maham Liaqat & Urooj Arif — Updated on May 2, 2024
Congruent shapes are identical in size and shape with corresponding sides and angles, whereas similar shapes have proportional sizes but identical angles.
Congruent vs. Similar — What's the Difference?

Difference Between Congruent and Similar

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Key Differences

Congruent shapes are exactly the same in both size and shape, meaning every corresponding side and angle matches. Whereas similar shapes maintain the same angle measurements, their side lengths are not necessarily the same but are proportional.
In congruence, the concept is often used in geometry to describe two or more objects where one can be perfectly superimposed on the other through translations, rotations, or reflections. On the other hand, similarity refers to shapes that look alike but differ in size, scalable through multiplication.
Triangles are a common focus in studying congruence and similarity. Congruent triangles have three identical sides and three identical angles. While similar triangles might only share the same angle measurements and have sides that are proportional, not identical.
In terms of application, congruent figures are crucial in fields requiring precise duplication, like engineering and architecture. Whereas similar figures are key in understanding scale and model building, where proportions maintain the essence but alter the scale.
Symbols also differ: congruence in geometric figures is denoted by the symbol ≅, emphasizing exact sameness. While similarity is denoted by the symbol ∼, indicating a likeness but not exact duplication.
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Comparison Chart

Definition

Exactly the same size and shape
Same shape, proportional sizes

Angle Correspondence

Identical angles
Identical angles

Side Length Correspondence

Identical side lengths
Proportional side lengths

Symbol

≅ (congruent to)
∼ (similar to)

Applications

Used in precise duplication (e.g., manufacturing)
Important in scale models and scaling applications

Compare with Definitions

Congruent

Identical in form and dimensions.
Two congruent squares fit perfectly on each other.

Similar

Proportionally equivalent in shape but not size.
The two similar triangles have sides that are scaled versions of each other.

Congruent

Having the exact same size and shape.
The two congruent circles overlapped without any gaps.

Similar

Having angles that are exactly alike.
Similar polygons exhibit the same angles but different side lengths.

Congruent

Equal in all geometrical aspects.
The congruent triangles can be rotated to match exactly.

Similar

Figures scaled up or down without altering shape.
A large and a small square are similar; one is just an enlargement of the other.

Congruent

Matching completely in terms of geometry.
Congruent angles in different polygons correspond exactly.

Similar

Corresponding in shape, differing in dimensions.
The similar rectangular prisms vary only in their overall size.

Congruent

Exactly superimposable figures.
The congruent rectangles share identical diagonals and angles.

Similar

Maintaining shape but varying in size.
The similar figures were used to demonstrate the concept of scaling in a math class.

Congruent

Corresponding; congruous.

Similar

Having a resemblance in appearance, character, or quantity, without being identical
Northern India and similar areas
A soft cheese similar to Brie

Congruent

Coinciding exactly when superimposed
Congruent triangles.

Similar

A person or thing similar to another
He was one of those whose similar you never meet

Congruent

Of or relating to two numbers that have the same remainder when divided by a third number. For example, 11 and 26 are congruent when the modulus is 5.

Similar

A substance that produces effects resembling the symptoms of particular diseases (the basis of homeopathic treatment)
The principle of treatment by similars

Congruent

Corresponding in character; congruous

Similar

Having a resemblance in appearance or nature; alike though not identical.

Congruent

Harmonious.

Similar

(Mathematics) Having corresponding angles equal and corresponding line segments proportional. Used of geometric figures
Similar triangles.

Congruent

(mathematics) Having a difference divisible by a modulus.

Similar

Having traits or characteristics in common; alike, comparable.
My new car is similar to my old one, except it has a bit more space in the back.

Congruent

(mathematics) Coinciding exactly when superimposed.

Similar

(mathematics) Of geometrical figures including triangles, squares, ellipses, arcs and more complex figures, having the same shape but possibly different size, rotational orientation, and position; in particular, having corresponding angles equal and corresponding line segments proportional; such that one can be had from the other using a sequence of rotations, translations and scalings.

Congruent

(algebra) Satisfying a congruence relation.

Similar

Of two square matrices; being such that a conjugation sends one matrix to the other.

Congruent

Possessing congruity; suitable; agreeing; corresponding.
The congruent and harmonious fitting of parts in a sentence.

Similar

That which is similar to, or resembles, something else, as in quality, form, etc.

Congruent

Corresponding in character or kind

Similar

(homeopathy) A material that produces an effect that resembles the symptoms of a particular disease.

Congruent

Coinciding when superimposed

Similar

Exactly corresponding; resembling in all respects; precisely like.

Similar

Nearly corresponding; resembling in many respects; somewhat like; having a general likeness.

Similar

Homogenous; uniform.

Similar

That which is similar to, or resembles, something else, as in quality, form, etc.

Similar

Marked by correspondence or resemblance;
Similar food at similar prices
Problems similar to mine
They wore similar coats

Similar

Having the same or similar characteristics;
All politicians are alike
They looked utterly alike
Friends are generaly alike in background and taste

Similar

Resembling or similar; having the same or some of the same characteristics; often used in combination;
Suits of like design
A limited circle of like minds
Members of the cat family have like dispositions
As like as two peas in a pod
Doglike devotion
A dreamlike quality

Similar

(of words) expressing closely related meanings

Similar

Capable of replacing or changing places with something else;
Interchangeable parts

Common Curiosities

What does it mean for two shapes to be congruent?

Two shapes are congruent if they are identical in size and shape, allowing them to fit perfectly on each other.

How do you prove that two triangles are similar?

Two triangles are similar if they have the same angles and their sides are in proportion.

How are similarity transformations different from those that preserve congruence?

Similarity transformations include rotations, translations, and reflections, as well as scaling (enlargement or reduction), which changes the size but not the shape.

Can two shapes be both congruent and similar?

Yes, congruent shapes are always similar because they have identical angles and proportional sides (in this case, the proportion is 1:1).

Why is it important for students to learn about congruence and similarity?

Understanding congruence and similarity helps students develop spatial reasoning, solve real-world problems involving dimensions, and comprehend the properties of different geometrical shapes.

How do similar shapes differ from congruent shapes?

Similar shapes have the same angles and proportional sides but differ in size, whereas congruent shapes are identical in both size and shape.

What is the significance of congruence and similarity in real life?

Congruence is vital in ensuring parts fit perfectly in manufacturing, while similarity helps in understanding scales and proportions in various fields like architecture and design.

What are the criteria for similarity of triangles?

Triangles are similar if they have corresponding angles equal and the sides around those angles in proportional lengths, satisfying angle-angle (AA) or side-angle-side (SAS) proportionality.

What geometric transformations preserve congruence?

Congruence is preserved through rotations, translations, and reflections, where the shape and size of figures remain unchanged.

How do you determine if two polygons are similar?

Two polygons are similar if their corresponding angles are equal and their corresponding side lengths are proportional.

How do congruence and similarity apply to symmetry in geometry?

Symmetry often involves congruence, where each symmetric part is identical in size and shape to its counterpart. Similarity relates to symmetry when scaling transformations are considered, maintaining shape but altering size.

Can circles be congruent or similar, and how?

All circles are similar as they differ only in size, not in shape. Circles are congruent when they have the same radius.

What are the criteria for congruence of triangles?

Triangles are congruent if they meet any of the following criteria: side-side-side (SSS), side-angle-side (SAS), or angle-side-angle (ASA).

In which professions is an understanding of congruence and similarity particularly useful?

Professions such as architecture, engineering, graphic design, and any field involving drafting or 3D modeling greatly benefit from an understanding of congruence and similarity.

What tools can be used to demonstrate congruence and similarity in a classroom setting?

Tools like geometric software, transparent overlays, geometric solids, and rulers and protractors can be used to visually and practically demonstrate the principles of congruence and similarity to students.

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Author Spotlight

Written by
Maham Liaqat
Co-written by
Urooj Arif
Urooj is a skilled content writer at Ask Difference, known for her exceptional ability to simplify complex topics into engaging and informative content. With a passion for research and a flair for clear, concise writing, she consistently delivers articles that resonate with our diverse audience.

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