Question

$-0,8 z^{2} +0,4z+2,4=0$

Answer 1

$-0,8z^2+0.4z+2.4=0\ -8z^2+4z+24=0\ 2z^2-z-3=0\ D=1+24=25\ |z=frac{1+5}{4}\ |z=frac{1-5}{4}\ \ |z=2.5\ |z=-1$

Answer 2

-0.8z²-0.4z+2.4=0
-1.25(-0.8z²-0.4z+2.4)=-1.25*0
z²+0.5z-3=0
D=0.5²-4*-3=0.25+12=12.25=3.5²
$z_{1}= frac{-0.5- sqrt{12.25} }{2*1}= frac{-0.5- 3.5 }{2} = frac{-4}{2} =-2 \ z_{2}= frac{-0.5+sqrt{12.25} }{2*1}= frac{-0.5+ 3.5 }{2} = frac{3}{2} =1.5$