Answer :

[tex]r^2 + 4r = 0\\ r(r+4)=0\\ r=0 \vee r=-4[/tex]
[tex]{ r }^{ 2 }+4r=0\\ \\ r\left( r+4 \right) =0\\ \\ \therefore \quad r=0\quad \wedge \quad r=-4[/tex]

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