For A to B, or segment AB, we have the points (1,1) and (4,3). (x1, y1) = (1,1) and (x2, y2) = (4,3);
x = 1 + t(4 - 1)
y = 1 + t(3 - 1)
A to B => (x = 1 + 3t, y = 1 + 2t)
We can apply a similar process for BC and AC. For BC we have (x1, y1) = (4,3) and (x2,y2) = (1,7);
x = 4 + t(1 - 4)
y = 3 + t(7 - 3)
B to C => (x = 4 - 3t, y = 3 + 4t)
(x1, y1) = (1, 1) and (x2, y2) = (1, 7);
x = 1 + t(1 - 1)
y = 1 + t(7 - 1)
A to C => (x = 1, y = 1 + 6t)
Here is your graph of the triangle. Desmos is a really great tool to use;