`a)\ 16x^2-(4x-5)^2=15`
`⇔16x^2-[(4x)^2-2*4x*5+5^2]-15=0`
`⇔16x^2-(16x^2-40x+25)-15=0`
`⇔16x^2-16x^2+40x-25-15=0`
`⇔40x-40=0`
`⇔40x=40`
`⇔x=40/40`
`⇔x=1`
Vậy `S={1}`
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`b)\ (2x+3)^2-4(x+1)(x-1)=49`
`⇔(2x)^2+2*2x*3+3^2-4(x^2-1^2)=49`
`⇔4x^2+12x+9-4x^2+4=49`
`⇔(4x^2-4x^2)+12x+9+4-49=0`
`⇔12x-36=0`
`⇔12x=36`
`⇔x=3`
Vậy `S={3}`
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`c)\ (2x+1)(1-2x)+(1-2x)^2=18`
`⇔(1+2x)(1-2x)+(1-2x)^2=18`
`⇔1^2-(2x)^2+1^2-4x+(2x)^2-18=0`
`⇔-4x^2+1+1-4x+4x^2-18=0`
`⇔(-4x^2+4x^2)+(1+1-18)-4x=0`
`⇔-4x-16=0`
`⇔-4x=16`
`⇔x=-4`
Vậy `S={4}`
.........................................
`d)\ (3x-1)^2-(3x-2)^2=0`
`⇔(3x-1-3x+2)(3x-1+3x-2)=0`
`⇔[(3x-3x)+(-1+2)][(3x+3x)+(-2-1)]=0`
`⇔1(6x-3)=0`
`⇔6x-3=0/1`
`⇔6x-3=0`
`⇔6x=3`
`⇔x=3/6`
`⇔x=1/2`
Vậy `S={1/2}`
