Toán Lớp 8: Tìm x,biết
b) x^3 + 0,25x = 0
c) x^2 – 10x = – 25
d) 4x^3 – 36x = 0
e) (5x – 4)^2 – 49x^2 = 0
f) (3x + 2)^2 – (x + 1)^2 = 0
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Toán Lớp 8: Tìm x,biết
b) x^3 + 0,25x = 0
c) x^2 – 10x = – 25
d) 4x^3 – 36x = 0
e) (5x – 4)^2 – 49x^2 = 0
f) (3x + 2)^2 – (x + 1)^2 = 0
Comments ( 2 )
$⇔x(x^2+0,25)=0$
$x^2≥0⇔x^2+0,25≥0,25$
$⇒x=0$
Vậy $x=0$
$⇔x^2-10x+25=0$
$⇔(x-5)^2=0$
$⇔x-5=0$
$⇔x=5$
Vậy $x=5$
d,
$⇔4x(x^2-9)=0$
$+,4x=0$
$x=0$
$+,x^2-9=0$
$x^2=9$
$x=±9$
Vậy S={±9;0}
$⇔(5x-4-7x)(5x-4+7x)=0$
$⇔-(2x+4)4(x-3)=0$
$2x=-4$
$x=-2$
$+,x-3=0$
$x=3$
Vậy S={-2;3}
$⇔(3x+2+x+1)(3x+2-x-1)=0$
$⇔(4x+3)(2x+1)=0$
$+,4x+3=0$
$⇔4x=-3$
$⇔x=\dfrac{-3}{4}$
$+,2x+1=0$
$⇔2x=-1$
$⇔x=\dfrac{-1}{2}$
Vậy S={\frac{-3}{4};\frac{-1}{2}}