Có:
\(a\left(a+b+c\right)=-12\)
\(b\left(a+b+c\right)=18\)
\(c\left(a+b+c\right)=30\)
=> \(a\left(a+b+c\right)+\)\(b\left(a+b+c\right)+\)\(c\left(a+b+c\right)=-12+18+30\)
\(\left(a+b+c\right)\left(a+b+c\right)=36\)
\(\left(a+b+c\right)^2=6^2\)
=>\(a+b+c=6\)
Có: \(a\left(a+b+c\right)=-12\)
=> \(6a=-12\)
a=-2
\(b\left(a+b+c\right)=18\Rightarrow6b=18\Rightarrow b=3\)
\(c\left(a+b+c\right)=30\Rightarrow6c=30\Rightarrow c=5\)
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