a) *Nếu x-1 >=0 <=> x>=1 thì |x-1|=x-1
=> 2(x-1)=3x-5
<=> 2x-2=3x-5
<=> 2x-3x=-5+2
<=> -x=-3
<=> x=3 ( TM )
*Nếu x-1<0 <=> x<1 thì |x-1|=1-x
=> 2(1-x) =3x-5
<=> 2-2x=3x-5
<=> -2x-3x=-5-2
<=> -5x=-7
<=> x= 7/5 ( K TM )
S={3}
b) x(x-1)=72
<=> x^2-x-72=0
<=> x^2-9x+8x-72=0
<=> (x^2-9x) + (8x-72) =0
<=> x(x-9) + 8(x-9) =0
<=> (x-9) + (x+8) =0
<=> x-9=0 hoặc x+8=0
<=> x=9 hoặc x=-8
S={9, -8}
