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Let ` vec a , vec b ,a n d vec c`are vectors such that `| vec a|=3,| vec b|=4a n d| vec c|=5,a n d( vec a+ vec b)`is perpendicular to ` vec c ,( vec b+ vec c)`is perpendicular to ` vec aa n d( vec c+ vec a)`is perpendicular to ` vec bdot`Then find the value of `| vec a+ vec b+ vec c|`. |
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Answer» Let `vec(a), vec(b), vec(c)` be the given vectors such that `{|vec(a)|=3, |vec(b)|=4, |vec(c)|=5}`, ...(i) `{:(vec(a).(vec(b)+vec(c))=0),(vec(b).(vec(c)+vec(a))=0),(vec(c).(vec(a)+vec(b))=0):}}`. ...(ii) `:. |vec(a)+vec(b)+vec(c)|^(2)=(vec(a)+vec(b)+vec(c)).(vec(a)+vec(b)+vec(c))` `=vec(a).vec(a)+vec(a).(vec(b)+vec(c))+vec(b).(vec(c)+vec(a))+vec(b).vec(b)+vec(c).(vec(a)+vec(b))+vec(c).vec(c)` `=|vec(a)|^(2)+|vec(b)|^(2)+|vec(c)|^(2)` [using (ii)] `=(3^(2)+4^(2)+5^(2))=(9+16+25)=50` Hence, `|vec(a)+vec(b)+vec(c)|=sqrt(50)=5sqrt(2)`. |
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