1.

The three vectors a, b and c with magnitude 3, 4 and 5 respectively and a+b+c=0, then the value of a.b+b.c+c.a is

Answer»

`-23`
`-25`
30
26

Solution :Given,`a+b+c=0`
On squaring both SIDES, we get
`|a+b+c|^(2)=0`
`RARR a^(2)+b^(2)+c^(2)+2(a*b+b*c+c*a)=0`
`rArr 2(a*b+b*c+c*a)=-(9+16+25)`
`THEREFORE a*b+b*c+c*a=-25`


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