Question

If a bar + b bar = c bar and c= root over a square + b square then angle between a bar and c bar

Answer 1

Correct option is

D

60

∘

Given

a

ˉ

+

b

ˉ

+

c

ˉ

=0 and ∣

a

ˉ

∣=3,∣

b

ˉ

∣=5,∣

c

ˉ

∣=7

Let angle between

a

ˉ

and

b

ˉ

be θ

a

ˉ

+

b

ˉ

+

c

ˉ

=0

⇒

a

ˉ

+

b

ˉ

=−

c

ˉ

⇒∣

a

ˉ

∣

2

+∣

b

ˉ

∣

2

+2

a

ˉ

⋅

b

ˉ

=∣

c

ˉ

∣

2

⇒9+25+30cosθ=49

⇒cosθ=

2

1

∴θ=

3

π

Hence, option D.