(a-4)*(a-5)-2a*(a-6)=

a^2-5a-4a+20-2a^2+12a=-a^2+3a+20

а*а+20-9а-2а*а+12а=3а-а*а+20=-а*а+3а-2,25+22,25=25*0,89-(а-1,5)^2=
(1,5+5sqrt(0,89)-a)*(a-1,5+5sqrt(0,89))