1.

If `hat(a) and hat(b)` are unit vectors such that `(hat(a) + hat(b))` is a unit vector, what is the angle between `hat(a) and hat(b)`?

Answer» Correct Answer - `(2pi)/(3)`
`(hat(a)+hat(b)).(hat(a)+hat(b))=1rArra^(2)+b^(2)+2hat(a).hat(b)=1`
`rArr1+1+2hat(a).hat(b)=1rArr2hat(a).hat(b)=-1`
`rArrhat(a).hat(b)=(-1)/(2)rArr|hat(a)||hat(b)|cos theta=(-1)/(2)`
`rArr cos theta = (-1)/(2)rArr theta=(2pi)/(3)`.


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