TRIANGLE
1.1. WHAT IS A TRIANGLE?
A triangle is a polygon with three sides having
three vertices. The angle formed inside the
triangle is equal to 180 degrees.
1.2. THEOREMS AND PROPERTIES
1. The sum of the three angles of a triangle is
equal to two right angles or 180.
2. The sum of two sides of a triangle is greater
than the third side, and their difference is
less than the third side.
3. Two triangles are said to be similar if the
corresponding angles are congruent and the
corresponding side lengths are proportional.
4. If two sides of a triangle are equal (an isosceles triangle),
the angles opposite these sides are equal.
5. If two sides of a triangle are unequal, the angles opposite are
unequal, and the greater angle is opposite the greater side
