Parallel lines have
the same slope.In any geometry problem, never assume that two lines are parallel unless the question or diagram
specifically tells you so. In the following diagram, angle a is a big angle, and it has the same
measure as angles c, e, and g, which are also big angles. Angle b is a small angle, and it has the
same measure as angles d, f, and h, which are also small angles.a = c = e = g
b = d = f = h
l 2 = l 3You should be able to see that the degree measures of angles a, b, c, and d add up to 360 degrees.
So do those of angles e, f, g, and h. If you have trouble seeing it, draw a circle around the angles.
What is the degree measure of a circle? Also, the sum of any small angle (such as d) and any big
angle (such as g) is 180°.Let’s see how these concepts might be tested on the SAT.