`hatA` तथा `hatB` एकांक सदिश है अतः `|hatA| = |hatB| =1`
`therefore |hatA -hatB| = sqrt(|hatA|^(2) + |hatB|^(2) -2|hatA||hatB| cos theta)`
`=sqrt((1)^(2) + (1)^(2) - 2(1)(1) cos theta)`
`=sqrt(2- 2 cos theta) = sqrt(2(1 - costheta) = sqrt(2 xx (2 sin ""(theta)/(2))`
` [therefore cos theta = 1 - 2 sin^(2) (theta)/(2)]`
`= 2 sin "" (theta)/(2)`
