If a and b are two unit vectors and a+b is also a unit vector then what is the angle between a and b

Hi Aparna,

You can answer this question in the following way:

Let the angle between the vectors be Φ

Thus we have the following relation:

 |a+b|² = |a|² + |b|² +2|a||b|cosΦ

As a and b and a+b are unit vectors |a|, |b|, |a+b| are 1

Thus solving we get: cosΦ = -0.5

Thus Φ=120^o

Topper Learning Team