Ответ:

Найти неизвестную величину .

[tex]\bf 8)\ \ 0,3m^2-3m+7,5=0\\\\D=b^2-4ac=9-9=0\\\\m=\dfrac{3}{0,6}=5\\\\\\9)\ \ x^2-2x+2=0\\\\D=4-8=-4 < 0\\\\x\in \varnothing \\\\\\10)\ \ -2x^2-0,5x+1,5=0\\\\D=0,25+12=12,25\\\\\sqrt{D}=3,5\\\\x_1=\dfrac{0,5-3,5}{-4}=0,75\ \ ,\ \ x_2=\dfrac{-0,5+3,5}{-4}=-0,75[/tex]    

[tex]\bf 11)\ \ 0,4x^2-2x+2,5=0\\\\D=4-4=0\\\\x=\dfrac{2}{0,8}=2,5\\\\\\12)\ \ -1,2m^2+2,6m-1=0\ \ \Big|\cdot (-5)\\\\6m^2-13m+5=0\\\\D=13^2-4\cdot 6\cdot 5=169-120=49\\\\\sqrt{D}=7\\\\m_1=\dfrac{13-7}{12}=\dfrac{1}{2}\ \ ,\ \ m_2=\dfrac{13+7}{12}=\dfrac{5}{3}[/tex]