If a and b are unit vectors and is the angle between them, then a+b is a unit vector when cos ⁡ =

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Correct answer: A. (a) Given that, |a |= |b |=1 and is the angle between a and b. cos ⁡ = a b |a | |b | cos =a b … . . (i ) Now, a+b is also unit vector, then |a+b |=1 |a+b |^2=1 (a+b ) (a+b )=1 |a |^2+2a b+ |b |^2=11+2 cos +1=1 [ using eq . (i ) ]1+2 cos ⁡ =0 cos ⁡ =- 12

$If a and b are unit vectors and α is the angle between them, then a + b is a unit vector when cos α =$

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