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प्रश्न
Find `|vecx|`, if for a unit vector veca , `(vecx - veca).(vecx + veca) = 12`.
उत्तर
We have, `(vecx - veca) xx (vecx + veca) = 12`
`vecx xx vecx + vecx xx veca - veca xx vecx - veca xx veca = 12`
`|vecx|^2 - |veca|^2 = 12` ....`[∵ vecx xx veca = veca xx vecx]`
`|vecx|^2 - 1 = 12 ...[∵ |veca| = 1]`
`|vecx|^2 = 13`
`|vecx| = sqrt13`
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