The coordinates of the vertices P, Q and R of a triangle PQR are (1, $$-$$1, 1), (3, $$-$$2, 2) and (0, 2, 6) respectively. If $$\angle$$RQP = $$\theta$$, then what is $$\angle$$PRQ equal to?

If the line $${{x - 4} \over 1} = {{y - 2} \over 1} = {{z - k} \over 2}$$ lies on the plane $$2x - 4y + z = 7$$, then what is the value of k?

A point on the line $${{x - 1} \over 1} = {{y - 3} \over 2} = {{z + 2} \over 7}$$ has coordinates

If the points (x, y, $$-$$3), (2, 0, $$-$$1) and C (4, 2, 3) lie on a straight line, then what are the values of x and y respectively?