1.

Let `veca` and `vecb` be two non-collinear unit vectors. If `vecu=veca-(veca.vecb)vecb` and `vec=vecaxxvecb`, then `|vecv|` isA. `|vecu|`B. `|vecu|+ |vecu.vecb|`C. `|vecu| + |vecu .veca|`D. none of these

Answer» Correct Answer - b,d
`vecu = vecas - ( veca . Vecb) vecb`
` vecb xx (veca xx vecb)`
` Rightarrow |vecu| = |vecb xx (veca xx vecb)|`
` |vecb| |veca xx vecb| sin 90 ^(@)`
` |vecb||veca xx vecb|`
` |vecv|`
Also ` vecu . Vecb = vecb.vecb xx (veca xx vecb)`
` [vecb vecb veca xx vecb]`
=0
` Rightarrow |vecv| = |vecu| + |vecu. vecb|`


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