Basic Angle Properties (CIE IGCSE Maths: Extended)

What are the basic angle properties?

• Angles that meet at a point add up to 360°
• Angles that meet at a point on a straight line add up to 180°
• Vertically opposite angles are equal
• Vertically opposite angles occur when two lines intersect
• They are the angles either side of the intersection that are opposite to each other

What are the angle properties with triangles?

• The three interior angles inside any triangle add up to 180°
• If the triangle is isosceles then two angles will be equal
• These will be the two angles opposite the two sides of equal length
• If the triangle is equilateral then the three angles will be equal
• Each angle will equal 60°

What are the angle properties with quadrilaterals?

• The four interior angles inside any quadrilateral add up to 360°
• If the quadrilateral is a square or a rectangle then all the angles are equal
• Each angle will equal 90°
• You can use any symmetries of the quadrilateral to identify other equal angles
• For a parallelogram or rhombus opposite angles are equal
• For a kite one pair of opposite angles are equal