2) =-5(x²-4x/5-1/5)=-5(x²-2*2x/5+4/25-4/25-5/25)=
=-5( (x²-2/5)² -9/25)=-5( (x-2/5)²-(3/5)² )=-5(x-2/5-3/5)(x-2/5+3/5)=
= - 5(x-1)(x+1/5)
3) =12(x²+5x/12-1/6)= 12(x²+2x*5/24 +5²/24²-5²/24²-1/6)
=12( (x+5/24)² -121/576) =12(x+5/24-11/24)(x+5/24+11/24))=
=12(x-6/24)(x+16/24)=12(х-1/4)(х+2/3)
4) =-21(x²-x/3+1/21)= -21(x²-2*x/(3*2) +1/6²-1/6²+1/21)=
=-21( (x-1/6)²-1/36+1/21) - не раскладывается на множители