Triangles

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A triangle is a closed figure formed by three intersecting lines. It has three sides, three angles, and three vertices. For example, in triangle ABC: AB, BC, CA are the three sides; ∠A, ∠B, ∠C are the

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Congruent figures are figures that have the same shape and size. They can cover each other completely when placed on top of each other. Examples: two coins of the same denomination, identical photogra

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Two triangles are congruent if all corresponding sides and angles are equal. The symbol ≅ means 'congruent to'. If △PQR ≅ △ABC, then PQ = AB, QR = BC, RP = CA and ∠P = ∠A, ∠Q = ∠B, ∠R = ∠C.

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When writing congruent triangles, the order of vertices must show the correct correspondence. If P↔A, Q↔B, R↔C, then we write △PQR ≅ △ABC. Writing △QRP ≅ △ABC would be incorrect because it doesn't sho

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CPCT stands for 'Corresponding Parts of Congruent Triangles'. It is used to state that when two triangles are congruent, their corresponding sides and angles are equal. This is often used in proofs af

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SAS Congruence Rule: Two triangles are congruent if two sides and the included angle of one triangle are equal to the two sides and the included angle of the other triangle. The angle must be between

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SSA (Side-Side-Angle) or ASS rule doesn't work because the angle is not included between the two equal sides. Two triangles can have two sides and one angle equal but still not be congruent if the ang

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ASA Congruence Rule: Two triangles are congruent if two angles and the included side of one triangle are equal to two angles and the included side of the other triangle. The side must be between the t