Angle facts
- Angles on a straight line add up to 180°. Angles around a point add up to 360°.
- Vertically opposite angles are equal.
- Angles in a triangle add up to 180°. Angles in a quadrilateral add up to 360°.
- Acute angles are less than 90°, right angles are 90°, obtuse angles are between 90° and 180°, and reflex angles are between 180° and 360°.
Parallel lines
- Alternate angles are equal (they make a Z shape).
- Corresponding angles are equal (they make an F shape).
- Co-interior angles add up to 180° (they make a C shape).
Triangles
- The two base angles of an isosceles triangle are equal.
- Each angle in an equilateral triangle is 60°.
- The exterior angle of a triangle equals the sum of the two opposite interior angles.
Giving reasons
- In the exam, give a reason for each step using the proper words, such as 'alternate angles are equal'. Don't write 'Z angles'.
Key terms
- Acute angle
- An angle less than 90°.
- Obtuse angle
- An angle between 90° and 180°.
- Reflex angle
- An angle between 180° and 360°.
- Vertically opposite angles
- The equal angles opposite each other where two straight lines cross.
- Alternate angles
- Equal angles on opposite sides of a line crossing two parallel lines (a Z shape).
- Corresponding angles
- Equal angles in matching positions on parallel lines (an F shape).
- Co-interior angles
- Angles between two parallel lines on the same side, which add up to 180° (a C shape).
- Isosceles triangle
- A triangle with two equal sides and two equal angles.