(4x + 1)(12x - 1)(3x + 2)(x+1) = 4
[(4x+1)(3x+2)][(12x-1)(x+1)]=4
(12x2+11x+2)(12x2+11x-1)=4
dat a=12x2+11x+2
khi do phuong trinh tro thanh:
a(a-3)=4
a2-3a-4=0
a2+a-4a-4=0
a(a+1)-4(a+1)=0
(a+1)(a-4)=0
=>a+1=0 hoac a-4=0
=>a=-1 hoac a=4
=>12x2+11x+2=-1 hoac 12x2+11x+2=4
+)12x2+11x+2=-1
=>12x2+11x+3=0
=>36x2+33x+12=0
=>36x2+33x+121/16+71/16=0
=>(6x+11/4)2=-71/16(vo li)
+)12x2+11x+2=4
=>12x2+11x-2=0
=>36x2+33x-6=0
=>36x2+33x+121/4-145/4=0
=>(6x+11/4)2=145/4
=>6x+11/4=(can 145)/2
...(tu lam tiep nha)