P(1, 2), Q(3, 4)
we find the slope dividing the y over the x, that is:
m = (4 - 2)/(3 - 1) = 2/2
m = 1
and then use the line equation for a point and slope:
y - y1 = m(x - x1)
where (x1, y1) is a point through which the line passes, we use P(1,2):
y - 2 = 2(x - 1)
y - 2 = 2x - 2
y = 2x
therefore the slope is 2 and the y-axis intercept is 0
