`a, (4-3x) (10x-5) =0`
`⇔4-3x=0` hoặc `10x-5=0`
`⇔x=4/3` hoặc `x=1/2`
`b, (x-3) (2x-1) = (2x-1) (2x+3)
`⇔(x-3)(2x-1)-(2x-1)(2x+3)=0`
`⇔(2x-1)(x-3-2x-3)=0`
`⇔2x-1=0` hoặc `-x-6=0`
`⇔x=1/2` hoặc `x=-6`
`c, (x+7) (3x+1)=49 -x^2`
`⇔3x^2+x+21x+7-49+x^2=0`
`⇔4x^2+22x-42=0`
`⇔2(x+7)(2x-3)=0`
`⇔-7` hoặc `3/2`
Vậy ...............................