Question

If $A , B , C , D$ are the points (2, 3, –1),(3, 5, –3), (1, 2, 3),

(3, 5, 7) respectively, then the angle between AB and CD is

• A. $\frac { \pi } { 2 }$
• B. $\frac { \pi } { 3 }$
• C. $\frac { \pi } { 4 }$
• D. $\frac { \pi } { 6 }$

Answer 1

Answer: (A)

$\frac { \pi } { 2 }$

Answer 2

D.r’s of AB ≡ $( 1,2 , - 2 )$, D.r’s of $C D \equiv ( 2,3,4 )$

∴ $a _ { 1 } a _ { 2 } + b _ { 1 } b _ { 2 } + c _ { 1 } c _ { 2 } = 0$; ∴ $\cos \theta = 0$ ⇒ $\theta = \pi / 2$.