b,
$x^3+0,25x=0$
$⇔x(x^2+0,25)=0$
$x^2≥0⇔x^2+0,25≥0,25$
$⇒x=0$
Vậy $x=0$
c,
$x^2-10x=-25$
$⇔x^2-10x+25=0$
$⇔(x-5)^2=0$
$⇔x-5=0$
$⇔x=5$
Vậy $x=5$
d,
$4x^3-36x=0$
$⇔4x(x^2-9)=0$
$+,4x=0$
$x=0$
$+,x^2-9=0$
$x^2=9$
$x=±9$
Vậy `S={±9;0}`
e,
$(5x-4)^2-49x^2=0$
$⇔(5x-4-7x)(5x-4+7x)=0$
$⇔-(2x+4)4(x-3)=0$
$+,2x+4=0$
$2x=-4$
$x=-2$
$+,x-3=0$
$x=3$
Vậy `S={-2;3}`
f,
$(3x+2)^2-(x+1)^2=0$
$⇔(3x+2+x+1)(3x+2-x-1)=0$
$⇔(4x+3)(2x+1)=0$
$+,4x+3=0$
$⇔4x=-3$
$⇔x=\dfrac{-3}{4}$
$+,2x+1=0$
$⇔2x=-1$
$⇔x=\dfrac{-1}{2}$
Vậy `S={\frac{-3}{4};\frac{-1}{2}}`