Types of triangles:
Equilateral triangle:
All sides have the same length. An equilateral triangle is also a regular polygon with all angles measuring 60°.
Isosceles triangle:
Two sides are equal in length.An isosceles triangle also has two angles of the same measure; namely, the angles opposite to the two sides of the same length.
Scalene triangle:
All sides and internal angles are different from one another.
Oblique triangle:
Triangles that do not have an angle that measures 90° are called oblique triangles.
Acute triangle:
A triangle that has all interior angles measuring less than 90° is an acute triangle or acute-angled triangle.
Obtuse triangle:
A triangle that has one angle that measures more than 90° is an obtuse triangle or obtuse-angled triangle.
Right triangle:
A right triangle (or right-angled triangle) has one of its interior angles measuring 90° (a right angle).
The side opposite to the right angle is the hypotenuse; it is the longest side in the right triangle.
The other two sides are the legs or catheti of the triangle.
Pythagorean theorem:
The sum of the squares of the lengths of the two legs is equal to the square of the length of the hypotenuse: a2 + b2 = c2, where a and b are the lengths of the legs and c is the length of the hypotenuse.