Given vertices of a △ABC are A(−1,3,2),B(2,3,5) and C(3,5,−2). Now DR's of AB=(2+1,3−3,5−2) =(3,0,3) DR's of BC=(3−2,5−3,−2−5) =(1,2,−7) and DR's of CA=(−1−3,3−5,2+2) =(−4,−2,4) Now, the angle between AB and BC, cos‌B‌=‌