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This essential trains for: SAT-I, GMAT, Math Kangaroo 5-6, Math Kangaroo 7-8.
Triangles are polygons with three angles (and three sides).
Sum of angles: The sum of the angles of a triangle is 180°.
Consequence: Only one angle of a triangle may be obtuse.
Triangle inequality: For three segments to form a triangle, any two of them must have a combined length that exceeds the length of the third one.
The line of symmetry of an isosceles triangle is also:
The lines of symmetry of an equilateral triangle are also:
Note: The plane may be tiled with equilateral triangles.
A right-angle triangle: is half of a rectangle.