Suppose ΔABC is a triangle. Then, depending on sides:

Equilateral Triangle:

AB=CD=AC

(all 3 sides of a triangle are equal)

Isosceles Triangle:

AB=AC or AB=BC or BC=AC

(any 2 sides of a triangle are equal)

Scalene Triangle:

None of the sides of a triangle are equal

Suppose the given diagram is a triangle (a+b+c=180°). Then, depending on angles:

Acute-Angled Triangle:

a<90°, b<90°, c<90°

(all 3 angles of a triangle are less than 90°)

Right-Angled Triangle:

a=90° or b=90° or c=90°

(any 1 angle of a triangle is 90°)

Obtuse-Angled Triangle:

a>90° or b>90° or c>90°

(any 1 angle of a triangle is more than 90°)