Question

plx help me exam is running

Answer 1

Answer:

see i definitely have forgot the concopt but will hep you in just a moment

Answer 2

Given A⃗ & B⃗ are unit vectors i.e. |A⃗|=|B⃗|=1

If θ is the angle between the unit vectors A⃗ & B⃗ then the vectors (A⃗+2B⃗) & (5A⃗−4B⃗) will be perpendicular if their dot product is zero hence

(A⃗+2B⃗)⋅(5A⃗−4B⃗)=0

5A⃗⋅A⃗+10A⃗⋅B⃗−4A⃗⋅B⃗−8B⃗⋅B⃗=0

5|A⃗|2+6A⃗⋅B⃗−8|B⃗|2=0

5+6A⃗⋅B⃗−8=0(∵ |A⃗|=|B⃗|=1)

A⃗⋅B⃗=36

|A⃗||B⃗|cosθ=12

1⋅1⋅cosθ=12

cosθ=12

cosθ=cos60∘

θ=60∘