Triangles

Definitions and properties of triangles in geometry.

Triangle A closed plane figure with three (straight) sides. The sum of all three interior angles of a triangle is equal to 180 degrees. Isosceles Triangle A triangle with two sides equal in size. Angles B and C are equal in size. Equilateral Triangle A triangle with all sides equal in size. All angles of the triangle are equal in size. Right Triangle A triangle with a right angle. c is the hypotenuse, a and b are the legs of the triangle. Pythagorean theorem: c 2 = a 2 + b 2 Sine law in a Triangle Triangle without right angle may be solved using sine law expressed as follows a / sin(A) = b / sin(B) = c / sin(C) Cosine law in a Triangle cosine law expressed as follows a 2 = b 2 + c 2 - 2 b c cos(A) or b 2 = a 2 + c 2 - 2 a c cos(B) or c 2 = b 2 + a 2 - 2 b a cos(C) More geometry references Triangle Problems Geometry Tutorials, Problems and Interactive Applets.

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