Let t = theta for short
Let L1 and L2 denote two nonvertical intersecting lines, and let theta t denote the acute angle between L1 and L2.
Show that tan(t) = (m2 - m1)/[1 + (m1)(m2)], where m1 and m2 are the slopes of L1 and L2, respectively.
HINT GIVEN BY TEACHER:
Use the facts that tan(t1) = m1 and tan(t2) = m2)