question_answer 1)

Show that the points (2, 3, 4), (–1, –2, 1), (5, 8, 7) are collinear. 

Answer:

Given points are A(2, 3, 4), B(?1, ?2, 1) and C(5, 8, 7).       Let directions ratios of lines AB and BC are a1, b1, c1 and c1 and a2, b2, c2                   and a2 = 5 ? (?1) = 6, b2 = 8 ? (?2) = 10, c2 = 7 ?1 = 6       Here       Clearly        lines AB and BC are parallel. But point B common.        points A, B, C are collinear.