x2 - 9= 2x +6
<=> x2 - 9 - 2x - 6 = 0
<=> x2-2x-15=0
<=> x2-5x+3x-15=0
<=> x(x-5) + 3(x-5)= 0
<=> (x-5)(x+3)=0
\(\Leftrightarrow\left[{}\begin{matrix}x-5=0\\x+3=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=5\\x=-3\end{matrix}\right.\)
Vậy: \(S=\left\{-3,5\right\}\)
x2-9=2x+6
\(\Leftrightarrow\)x2-9-2x-6=0
\(\Leftrightarrow\)x2-2x-15=0
\(\Leftrightarrow\)x2-5x+3x-15=0
\(\Leftrightarrow\)x(x-5)+3(x-5)=0
\(\Leftrightarrow\)(x-5)(x+3)=0
\(\Leftrightarrow\left[{}\begin{matrix}x-5=0\\x+3=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=5\\x=-3\end{matrix}\right.\)
Vậy pt có tập nghiệm S =\(\left\{5;-3\right\}\)
x2 - 9 = 2x + 6
x2-2x-9-6=0
x2-2x-15=0
x2+3x-5x-15=0
x(x+3)-5(x+3)=0
(x-5)(x+3)=0
\(\left\{{}\begin{matrix}x-5=0\\x+3=0\end{matrix}\right.\left\{{}\begin{matrix}x=5\\x=-3\end{matrix}\right.\)
vậy ...
=) x^2 -2x -9-6=0
=) x^2 -2x-15=0
=) x^2 -5x+3x-15=0
=) x(x-5)+ 3(x- 5)=0
=) (x-5).(x+3)= 0
[ x-5= 0 =)x=5
[ x +3 = 0=) x= -3
=) x^2 -2x -9-6=0
=) x^2 -2x-15=0
=) x^2 -5x+3x-15=0
=) x(x-5)+ 3(x- 5)=0
=) (x-5).(x+3)= 0
[ x-5= 0 =)x=5
[ x +3 = 0=) x= -3
