A line that inclines at 45 degrees has a slope of 1. Think of the line y=x and how it passes through the origin at 45 degrees relative to the x-axis.
Since you are taking trig, you can also find the slope by taking the tan 45 degrees. This is consistent with tan m = y/x for coordinate (x,y) with slope m. For the point (1,1), m=1.
Hope this helps