a)2x² + 4x=0
=>2x(x+2)=0
=>\(\left[ \begin{array}{l}2x=0\\x+2=0\end{array} \right.\)
=>\(\left[ \begin{array}{l}x=0\\x=-2\end{array} \right.\)
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b)x² +6x +9=0
=>(x+3)²=0
=>x+3=0
=>x=-3
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c)x²-14x+13=0
=>x²-13x-x+13=0
=>(x²-13x)-(x-13)=0
=>x(x-13)-(x-13)=0
=>(x-1)(x-13)=0
=>\(\left[ \begin{array}{l}x-1=0\\x-13=0\end{array} \right.\)
=>\(\left[ \begin{array}{l}x=1\\x=13\end{array} \right.\)
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