a) Ta có : (x-26)/24-1+(x-25)/25-1=(x-24)/26-1+(x-23)/27-1 ( trừ cả hai vế cho 1 )
x-50/24+x-50/25=x-50/26+x-50/27
x-50/24+x-50/25-x-50/26- x-50/27=0
(x-50)(1/24+1/25-1/26-1/27)=0
x-50=0
x=50
b) ta có 1/x^2-3x+2
=1/x^2-x-2x+2
=1/x(x-1)-2(x-1)
=1/(x-2)(x-1)
CMTT 1/x^2-5x+6=1/(x-2)(x-3)
CMTT 1/x^2-7x+12=1/(x-3)(x-4)
CMTT 1/x^2-9x+20=1/(x-4)(x-5)
Thay vào ta có 1/x-1-1/x-5=1/15
suy ra x-1-x+5=15
4=15 (vô lý )