Question

The co-ordinates of points A, B, C, D are (a, 2, 1), (1, –1, 1),

(2, –3, 4) and (a + 1, a + 2, a + 3) respectively. If AB = 5 and CD = 6, then a =

• A. 2
• B. 3
• C. –2
• D. –3

Answer 1

Answer: (D)

–3

Answer 2

AB =$\sqrt{4 + 1 + 4}$ = 3

AC = $\sqrt{144 + 16 + 9}$= 13

$D\left( \frac{–27 + 65}{3 + 13},\frac{18 + 39}{3 + 13},\frac{- 9 + 26}{3 + 13} \right)$=$\left( \frac{19}{8},\frac{57}{16},\frac{17}{16} \right)$