Hoặc
c) x+1x2−5x+x−18x2−5x+x+2x2−5x;
c) x+1x2−5x+x−18x2−5x+x+2x2−5x
=x+1+x−18+x+2x2−5x
=(x+x+x)+(1−18+2)x(x−5)
=3x−15x(x−5)=3(x−5)x(x−5)=3x;