If ` veca , vecb` are unit vectors such that ` |vec a+vecb|=-1 " then " |2veca -3vecb| =`A. 19B. `sqrt19`C. `sqrt13`D. 4

If ` veca , vecb` are unit vectors such that ` |vec a+vecb|=-1 " then

1.	If ` veca , vecb` are unit vectors such that ` \|vec a+vecb\|=-1 " then " \|2veca -3vecb\| =`A. 19B. `sqrt19`C. `sqrt13`D. 4
Answer» Correct Answer - B we have, `\|veca +vecb\|=1` ` Rightarrow \|veca\|^(2) +\|vecb\|^(2) + 2(veca .vecb) =1 ` ` Rightarrow 1+1 +2 (veca.vecb) =1 Rightarrow veca.vecb= -1/2 ` Now, ` \|2 veca -3 vecb\|^(2) =4 \|veca\|^(2) +9\|vecb\|^(2) -12(veca.vecb)` ` Rightarrow \|2veca -3vecb\|^(2) =4+9 =19` ` Rightarrow \|2veca -3vecb\|= sqrt19`

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If ` veca , vecb` are unit vectors such that ` |vec a+vecb|=-1 " then " |2veca -3vecb| =`A. 19B. `sqrt19`C. `sqrt13`D. 4

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