23. a) Notez x^2+x=t
t(t+1)-2=t^2+t-2=t^2+2t-t-2=t(t+2)-(t+2)=(t+2)(t-1)=(x^2+x+2)(x^2+x-1)
b) Notez x^2-x=t
t(t-1)-6=t^2-t-6=t^2-3t+2t-6=t(t-3)+2(t-3)=(t-3)(t+2)=(x^2-x-3)(x^2-x+2)
c)Notez x^2-3x=t
t(t-2)-3= t^2-2t-3=t^2-3t+t-3=t(t-3)+t-3=(t-3)(t+1)=(x^2-3x-3)(x^2-3x+1)
d) 2x^2+x=t
t(t-4)-5=t^2-4t-5=t^2-5t+t-5=t(t-5)+t-5=(t-5)(t+1)=(2x^2+x-5)(2x^2+x+1)
