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प्रश्न
If `hata` and `hatb` are unit vectors, then prove that `|hata + hatb| = 2 cos theta/2`, where θ is the angle between them.
उत्तर
`(hata + hatb).(hata + hatb) = |hata|^2 + |hatb|^2 + 2(hata.hatb)`
`|hata + hatb|^2 = 1 + 1 + 2costheta`
= `2(1 + cos theta) = 4cos^2 theta/2`
∴ `|hata + hatb| = 2cos theta/2`
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