a: Khi m=1 thì pt sẽ là x^2-2x-3=0
=>x=3 hoặc x=-1
b: (x1^2-mx1+m)(x2^2-mx2+m)=2
=>(x1x2)^2-m*x1^2*x2+m*x1^2-m*x1*x2^2+m^2*x1x2-x1*m^2+m*x2^2-m^2*x2+m^2=2
=>(x1x2)^2+m(-x1^2*x2+x1^2-x1*x2^2+x2^2)+m^2(x1x2-x1-x2)+m^2=2
=>(x1x2)^2+m[-x1x2(x1+x2)+(x1+x2)^2-2x1x2]+m^2[m+1-m+4]+m^2=2
=>(x1x2)^2+m[-(m-4)(m+1)+(m+1)^2-2(m-4)]+6m^2=2
=>(x1x2)^2+m[-m^2+3m+4+m^2+2m+1-2m+8]+6m^2=2
=>(x1x2)^2+m[3m+13]+6m^2=2
=>(m-4)^2+6m^2+13m-2=0
=>m^2-8m+16+6m^2+13m-2=0
=>7m^2+5m+14=0
=>Loại