Question

what is the angle between a 4 unit vector and a 5 unit vector so that there sum is 8 units​

Answer 1

Answer:

b

∣=1

∣

a

∣

2

+∣

b

∣

2

+2∣

a

∣∣

b

∣cosθ

=1

→2(1+cosθ)=1

→cosθ=

2

−1

θ=120

∘

∣

a

+

b

∣=

∣

a

∣+∣

b

∣

2

−2∣

a

∣∣

b

∣cosθ

=

1+1−2cos120

∘

=

2+2×

2

1

=

3

.