The non-zero vectors $\vec{a}, \vec{b}$ and $\vec{c}$ are related by $\vec{a}=8 \vec{b}$ and $\vec{c}=-7 \vec{b}$. Then the angle between $\vec{a}$ and $\vec{c}$ is

JEE Main · 2008 · 27 Apr 2008 · Offline · Vector Algebra

The non-zero vectors

a, b

and

c

are related by

a = 8 b

and

c = - 7 b

. Then the angle between

a

and

c

Answer: (D)

Since

a = 8 b

and

c = - 7 b

, both

a

and

c

are scalar multiples of the same vector

b

a

points the same way as

b

while

c

points opposite to it. Being parallel but oppositely directed,

a

and

c

make an angle of

π

between them.

JEE Main · 2008 · 27 Apr 2008 · Offline · Single correct option