Let `veca , vecb , vecc` be three unit vectors such that ` |veca + vecb +vecc| =1 and veca bot vecb , " if " vecc` makes angles ` delta beta " with " veca, vecb` respectively, then ` cos delta + cos beta ` is equal toA. 1B. -1C. `3/2`D. 0

Let `veca , vecb , vecc` be three unit vectors such that ` |veca + vec

1.	Let `veca , vecb , vecc` be three unit vectors such that ` \|veca + vecb +vecc\| =1 and veca bot vecb , " if " vecc` makes angles ` delta beta " with " veca, vecb` respectively, then ` cos delta + cos beta ` is equal toA. 1B. -1C. `3/2`D. 0
Answer» Correct Answer - B we have ` veca bot vecb` , therefore, ` veca.vecb =0` Also, `vecc. Veca = cos delta and vecc. Vecb =cos beta` . now , ` \|veca + vecb + vecc\|= 1` `Rightarrow \|veca + vecb + vecc\|^(2) =1` ` Rightarrow \|veca\|^(2) + \|vecb\|^(2) + \|vecc\|^(2) + 2 (veca.vecb + vecb.vecc + vecc.veca) =1` ` Rightarrow 1+1+1+2 ( cos delta + cos beta) =1` ` Rightarrow cos delta + cos beta = -1`

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