Объяснение:

7.

[tex]\frac{6}{x^2}-\frac{12}{x}=3\ |*(x^2).\ \ \ \ \ \ x\neq 0\\6-12*x=3*x^2 \\ 3x^2+12x-6=0\ |:3\\x^2+4x-2=0\\D=24\ \ \ \ \sqrt{D}=2\sqrt{6} .\\ x_1=\frac{-4-2\sqrt{6} }{1*2}=-2-\sqrt{6} \in .\\x_2=\frac{-4+2\sqrt{6} }{2} =-2+\sqrt{6} \in.[/tex]

8.

[tex]x^2-mx+3=0\ \ \ \ x_1=-0,6\ \ \ \ \ x_2=?\ \ \ \ m=?\\\left \{ {{-(x_1+x_2)=-m\ *(-1)} \atop {x_1*x_2=3}} \right. \ \ \ \ \left \{ {{-0,6+x_2=m} \atop {-0,6*x_2=3\ |:(-0,6)}} \right. \ \ \ \ \ \left \{ {{-0,6+(-5)=m} \atop {x_2=-5}} \right. \ \ \ \ \ \left \{ {{m=-5,6} \atop {x_2=-5}} \right. .[/tex]

Ответ: x₂=-5,   m=-5,6.