Lines, Angles & Shapes

Complementary Angles

• Adds up to 90°

• Adjacent complementary angles share a common vertex and arm

• Eg. B1 + B2 = 90° (Adj comp angles)

Supplementary Angles

• Adds up to 180°

• Adjacent supplementary angles share a common vertex and arm

• Eg. B1 + B2 = 180° (Adj suppl angles)

Angles on a straight line

• If ABC is a straight line then:

  • B1 + B2 = 180° (Angles on a str line)

• If B1 + B2 = 180°:

  • Then ABC is a straight line (Adj suppl angles)

Vertically opposite Angles

• If two lines intersect, then the vertically opposite angles are equal

• Eg:

  • E1 = E3 (Vert opp angles)

  • E2 = E4 (Vert opp angles)

Angles round a point

• Angles round a point add up to 360°

• Eg. B1 + B2 + B3 + B4 = 360° (Angles round a point)

Labeling angles

• Always label angles with 3 letters

  • ABC

  • Make sure to put a hat on the middle letter

Corresponding Angles (FUN Angle ‘F’)

• Lies either both above or both bellow the parallel lines and on the same side as the transversal

• They are the angles in matching corners and are equal

• Look out for the ‘F’ shape

• Eg:

  • If AB||CD then G1 = H1 (Corresp angles ; AB||CD)

  • If G1 = H1 then AB||CD (Corresp angles)

Co - Interior Angles (FUN Angles ‘U’)

• Lie on the same side of the transversal between the parallel lines

• When added together they = 180°

• Look out for the ‘U’ shape

• Eg:

  • If AB||CD then G1 + H1 = 180° (Co-int angles ; AB||CD)

  • If G1 + H1 = 180° then AB||CD (Co-int angles suppl)

Alternate Angles (FUN Angles ‘N’ or ‘Z’)

• Lie on opposite sides of the transversal and between the parallel lines

• They are equal in size

• Look out for the ‘Z’ or ‘N’ shape

• Eg:

  • If AB||CD then G1 = H1 (Alt angles ; AB||CD)

  • If G1 = H1 then AB||CD (Alt angles)