5x^2+21x+4=0
D=21^2-4*5*4=441-80=361
x1=(19-21)/(2*5)=-2/10=-0.2x2=(-19-21)/(2*5)=-40/10=-4
-x^2+12x+45=-(x-15)*(x+3)=(15-x)*(x+3)
5x^2+21x+4=0
D=21^2-4*5*4=441-80=361
x1=(19-21)/(2*5)=-2/10=-0.2
x2=(-19-21)/(2*5)=-40/10=-4
-x^2+12x+45=-(x-15)*(x+3)=(15-x)*(x+3)