Definition:Any two sides which have a common end point are known as Adjacent Sides
In the following Figure
Ponts "A" is a common end point of lines AB & AC, hence Lines AB & AC are Adjacent Sides.
Ponts "B" is a common end point of lines AB & BD, hence Lines AB & BD are Adjacent Sides.
Ponts "D" is a common end point of lines BD & DC, hence Lines BD & DC are Adjacent Sides.
Ponts "C" is a common end point of lines DC & CA, hence Lines DC & CA are Adjacent Sides.
Let study following figure also and find all Adjacent Sides:
Figure 1:
In the above figure, following are the pair of adjacent sides.
PQ & PS
PQ & QR
QR & RS
RS & SP
Figure 2:
In the above figure, following are the pair of adjacent sides.
ED & DC
DC & CB
CB & BA
BA & AF
AF & FE
FE & ED

