Ding the cosines of the angle B of the triangle formed by joining the points A(6,11,2). , B(1,-1,2) and C(1,2,6)

We have, A6,11,2; B1,-1,2; C1,2,6 as the vertices of ABC.Let AB = c; BC = A; CA = bUsing distance formula :AB = c = 6-12+11+12+2-22 = 13 unitsBC = a = 1-12+2+12+6-22 = 5 unitsCA = b = 6-12+11-22+2-62 = 122 unitsNow, cos B = a2+c2-b22accos B=25+169-1222×5×13 = 722×5×13=3665

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