1. \(\overline{OA}\) = (3 – 1)i + (-1 – 2)j + (7 – 3)k = 2i – 3j + 4k
\(\overline {OB}\) = (2 – 1)i + (4 – 2)j +(2 – 3)k = i + 2j – k
\(\overline {OC}\)= (4 – 1)i + (1 – 2 )j + (5 – 3 )k = 3i – j + 2 k.
2. From the figure,
3. Let the vertex of D be (x , y , z),
Then, \(\overline {OD}\) = (x – 1)i + (y – 2)j + (z – 3)k.
But we have,
\(\overline {OD}\)= 6i – 2j + 5k = (x – 1)i + (y – 2)j +(z – 3)k
x – 1 = 6 ⇒ x = 7, y – 2 = -2 ⇒ y = 0, z – 3 = 5 ⇒ z = 8.