Two angles whose sum, is 180∘ are called supplementary angles. Four angles are formed at the intersection of two lines. How many pairs of supplementary angles and equal angles are formed?
Four pairs of supplementary and two pairs of equal angles.
Consider two lines intersecting as shown.
At the intersection of two lines, sum of angles on one side of a line is 180∘. Consider 'line 1', on one side lies angles 'a' and 'd', and on the other side lies 'b' and 'c'. Similarly, consider 'line 2', on one side we have angles 'a' and 'b', and on the other side we have 'd' and 'c'.
So, totally we have four pairs of supplementary angles
a & d,
b & c,
a & b
'd' & 'c'.
Secondly, opposite angles are equal at the intersection of two lines. Here 'a & c' and 'b & d' are opposite pairs, and they are equal. So, there are two pairs of equal angles.