Let →a,→b,→c be vectors of length 3,4 and 5 respectively. Let →a be perpendicular to (→b+→c),→b to (→c+→a) and →c to (→a+→b). Find the length of the vector →a+→b+→c.
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Solution
Given, |→a|=3,|→b|=4,|→c|=5
Again →a⊥(→b+→c)
→a.(→b+→c)=0 ....(1)
→b⊥(→c+→a)
→b.(→c+→a)=0 ....(2)
→c(→a+→b)
→c.(→a+→b)=0 ....(3)
Adding (1), (2) and (3), we get
2(→a.→b+→b.→c+→c.→a)=0
Now |→a+→b+→c|2=|→a|2+|→b|2+|→c|2+2(→a.→b+→b.→c+→c.→a)