A triangle is a close figure which is bounded by three sides.

A

B C

Scalene triangle Isosceles triangle Equilateral triangle

Acute Angled Triangle Right Angled Triangle Obtuse Angled Triangle

Two geometrical figures are said to be congruent if they have exactly the same shape and size.

The symbol of congruence is “ ”

The line segments are congruent if and only if their lengths are equal.

A B C D

Two angles are congruent if and only if their measures are equal.

B

A C

E

D F

Two triangles are congruent if and only if one of them can be made to superpose on the other, so as to cover it exactly.A

B C

D

E F

ABC≡ DEF