It is veri easy
1 task ( I will solve them without formulas.)
[tex]x^{2}[/tex]-5х+4=
=([tex]x^{2}[/tex]-х)+(-4х+4)=
=х(х-1)-4(х-1)= [ There is a common multiplier. ]
=(х-1)(х-4)=
=(х-4)(х-1)
2 task
[tex]x^{3}[/tex]+1=
=[tex]x^{3}[/tex]
-[tex]x^{2}[/tex]+[tex]x^{2}[/tex]+х-х+1=
=([tex]x^{3}[/tex]-[tex]x^{2}[/tex]+х)+[tex]x^{2}[/tex]-х+1=
=х([tex]x^{2}[/tex]-х+1)+([tex]x^{2}[/tex]-х+1)=
=(х+1)([tex]x^{2}[/tex]-х+1)
3 task
[tex]x^{4}[/tex]-5[tex]x^{2}[/tex]+4=
=[tex]x^{4}[/tex]-4[tex]x^{2}[/tex]-[tex]x^{2}[/tex]+4=
=[tex]x^{2}[/tex]([tex]x^{2}[/tex]-4)-1([tex]x^{2}[/tex]-4)=
=([tex]x^{2}[/tex]-4)([tex]x^{2}[/tex]-1)=(х-2)(х+2)(х-1)(х+1)