Triangles part Two. Congruence and Similarity | iCalculator™ (2024)

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There are lessons in this math tutorial covering . The tutorial starts with an introduction to and is then followed with a list of the separate lessons, the tutorial is designed to be read in order but you can skip to a specific lesson or return to recover a specific math lesson as required to build your math knowledge of . you can access all the lessons from this tutorial below.

In this Math tutorial, you will learn:

  • What is the relationship between the sides and angles in a triangle?
  • What is the range of possible values for the side lengths in a triangle?
  • What are the conditions for two triangles to be congruent?
  • What are the conditions for two triangles to be similar?
  • What is the midline of a triangle?
  • What relationship does the Pythagorean Theorem point out?
  • What are the Euclidean Theorems? What can you find by using them?
  • What is Heron's Formula and why do we use it?
  • What is the relationship between elements in an isosceles triangle?
  • What special feature does a right triangle with angles 30° - 60° - 90° have?

Introduction

Triangles are very extensive in theory and application. Therefore, one tutorial is insufficient to explain all properties of triangles. This tutorial focuses on concepts such as congruence and similarity - concepts that deal with the comparison between triangles. It is a continuation of the previous chapters in a more extended approach.

Congruence and similarity are two important concepts in geometry that describe the relationship between two triangles. Congruence refers to the exact match between two triangles where all the sides and angles are of equal measure. In other words, if two triangles are congruent, they have the same size and shape. On the other hand, similarity refers to the proportionate match between two triangles where the angles are equal but the sides may be of different lengths. In other words, if two triangles are similar, they have the same shape but not necessarily the same size. Both congruence and similarity play an important role in geometry and help us to better understand and analyze geometric figures. Therefore, let's begin to explore this important topic of geometry.

Please select a specific "Triangles part Two. Congruence and Similarity" lesson from the table below, review the video tutorial, print the revision notes or use the practice question to improve your knowledge of this math topic.

Angles and Geometrical Figures Learning Material
Tutorial IDMath Tutorial TitleTutorialVideo
Tutorial
Revision
Notes
Revision
Questions
18.4Triangles part Two. Congruence and Similarity
Lesson IDMath Lesson TitleLessonVideo
Lesson
18.4.1Relations Between the Angles and the Sides of a Triangle
18.4.2Congruence of Triangles
18.4.3Similarity of Triangles
18.4.4Midline of a Triangle
18.4.5Pythagorean Theorem
18.4.6Euclidian Theorems
18.4.7Heron's Formula
18.4.8Two Special Theorems

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  5. Continuing learning angles and geometrical figures - read our next math tutorial: Quadrilaterals

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    Triangles part Two. Congruence and Similarity | iCalculator™ (2024)

    FAQs

    What are congruence and similarity of triangles? ›

    From the basic concepts of triangles we know that the two triangles are said to be congruent if they are of the same shape and size whereas two triangles are said to be similar if they are of the same shape but can be of different sizes. Similar triangles have the same proportions.

    What is the congruence of two triangles? ›

    Theorem: In two triangles, if the three sides of one triangle are equal to the corresponding three sides (SSS) of the other triangle, then the two triangles are congruent.

    How do you know if two triangles are similar or congruent? ›

    Congruent triangles have both the same shape and the same size. In the figure below, triangles A B C ‍ and D E F ‍ are congruent; they have the same angle measures and the same side lengths. Similar triangles have the same shape, but not necessarily the same size.

    How to know if it is congruent or not? ›

    Two shapes are congruent if they have the same shape and size. We can also say if two shapes are congruent, then the mirror image of one shape is the same as the other.

    How to find congruence and similarity? ›

    Figures are considered to be both congruent and similar if they are both the same size and the same shape, regardless of orientation. They may be rotated or flipped, but as long as the size, shape, and angles are all maintained, the objects are considered both congruent and similar. Top shapes are similar.

    What is an example of two triangles are congruent? ›

    If the three angles and the three sides of a triangle are equal to the corresponding angles and the corresponding sides of another triangle, then both the triangles are said to be congruent. In Δ PQR and ΔXYZ, as shown below, we can identify that PQ = XY, PR = XZ, and QR = YZ and ∠P = ∠X, ∠Q = ∠Y and ∠R = ∠Z.

    What are the rules of similarity? ›

    AA similarity criterion states that if any two angles in a triangle are respectively equal to any two angles of another triangle, then they must be similar triangles. AA similarity rule is easily applied when we only know the measure of the angles and have no idea about the length of the sides of the triangle.

    How to prove congruence of triangles? ›

    If two pairs of corresponding angles and the pair of included sides are congruent, then the triangles are congruent. If two pairs of corresponding angles and a pair of non-included sides are congruent, then the triangles are congruent.

    What is the rule of congruence? ›

    SAS Congruence Rule

    SAS stands for Side-Angle-Side. A triangle is said to be congruent to each other if two sides and the included angle of one triangle is equal to the sides and included angle of the other triangle. This axiom is an accepted truth and does not need any proofs to support the criterion.

    What makes two triangles similar? ›

    Similar triangles are triangles that have the same shape, but their sizes may vary. All equilateral triangles, squares of any side lengths are examples of similar objects. In other words, if two triangles are similar, then their corresponding angles are congruent and corresponding sides are in equal proportion.

    What is the symbol for congruence? ›

    A symbol commonly used for congruence is an equals symbol with a tilde above it, ≅, corresponding to the Unicode character 'approximately equal to' (U+2245). In the UK, the three-bar equal sign ≡ (U+2261) is sometimes used.

    How to tell if a triangle is not congruent? ›

    A triangle only has ‍ sides and ‍ angles. If we know ‍ distinct side measures or ‍ distinct angle measures, then we know the two triangles cannot be congruent.

    How to use coordinates to determine if two triangles are congruent? ›

    Given two triangles on a coordinate plane, you can check whether they are congruent by using the distance formula to find the lengths of their sides. If three pairs of sides are congruent, then the triangles are congruent by the above theorem.

    What are examples of congruent? ›

    The length of line segment AB is equal to 5 cm and PQ is also equal to 5 cm. Hence, the length of both line segments are equal to each other. So, if two or more lines are equal in length, they are said to be congruent to each other. Hence, the line segments AB and PQ are congruent with each other.

    What is congruence vs similarity test? ›

    Two shapes are said to be congruent if they are the same shape and size: that is, the corresponding sides of both shapes are the same length and corresponding angles are the same. The two triangles shown here are congruent. Shapes which are of different sizes but which have the same shape are said to be similar.

    What is an example of congruence in math? ›

    If two figures can be placed precisely over each other, they are said to be 'congruent' figures. If you place one slice of bread over the other, you will find that both the slices are of equal shape and size. The term “congruent” means exactly equal shape and size.

    What are congruence similarity statements? ›

    Writing Similarity Statements to Match Similar Sides and Angles: Vocabulary. Similar Triangles: Two triangles are called similar triangles if corresponding angles are congruent, and the ratios of corresponding sides are constant. Congruent Angles: Two angles are called congruent if they have the exact same measure.

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