ÐABD

is the complement of

ÐCBD

Ð QRP

is the supplement of

ÐSRP

When two straight lines cross, the angles on opposite sides of the vertex are called vertically opposite angles.

Corresponding angles correspond in position

E.g. ÐABC and ÐADE ÐABE and ÐACD

Corresponding angles are equal on parallel lines.

Alternate angles lie on either side of the crossing line (traversal) between parallel lines.

e.g. ÐABC and Ð BCD

are alternate angles

e.g. ÐABC and Ð BCD

are alternate angles

Alternate angles are equal between parallel lines.