Part A:
The
parametric equations

and

where

describes the line segment that joins the points

and

.
The parameterization of the line joining points A(1, 1) and B(5, 3) are given by substituting

.
Thus, we have
x = 1 + (5 - 1)t = 1 + 4t
y = 1 + (3 - 1)t = 1 + 2t
Therefore, the parameterization of line joining points A(1, 1) and B(5, 3) are x = 1 + 4t and y = 1 + 2t.
Part B:
The
parametric equations

and

where

describes the
line segment that joins the points

and

.
The parameterization of the line joining
points B(5, 3) and C(1, 7) are given by substituting

.
Thus, we have
x = 5 + (1 - 5)t = 5 - 4t
y = 3 + (7 - 3)t = 3 + 4t
Therefore, the parameterization of line joining points B(5, 3) and C(1, 7) are x = 5 - 4t and y = 3 + 4t.
Part C:
The
parametric equations

and

where

describes the
line segment that joins the points

and

.
The parameterization of the line joining
points C(1, 7) and A(1, 1) are given by substituting

.
Thus, we have
x = 1 + (1 - 1)t = 1
y = 7 + (1 - 7)t = 7 - 6t
Therefore, the parameterization of line joining points A(1, 1) and B(5, 3) are x = 1 and y = 7 - 6t.