Toán 8 Tìm x biết

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a) 25$x^2$ - 2 = 0
<=> $(5x)^2$ - ($\sqrt{2}^2$ = 0
<=> (5x - $\sqrt{2}$)(5x + $\sqrt{2}) = 0$
b) $x^2$ - 25 = 6x - 9
<=> $x^2$ - 8x + 2x -16 = 0
<=> x(x-8) + 2(x-8) = 0
<=> (x+2)(x-8)=0
c) $(2x-1)^2$ - (2x+5)(2x-5) = 18
<=> $4x^2$ - 4x + 1 - ($4x^2$ - 25) =18
<=>-4x = -8
d)$ 5x(x-3) -2x + 6 = 0
<=> 5x(x-3) -2(x-3) =0
<=> (5x-2)(x-3) = 0$
e) $(x+2)^2$ -(x+2)(x-2) = 0
<=>(x+2)(x+2 - x +2) =0
f) $(2x+3)^2$ - $(x - 1)^2$ = 0
<=> ( 2x+3-x+1)(2x+3+x-1) = 0
g) $x^3$ - 8 = $(x-2)^3$
<=> (x-2)($x^2$ + 2x + 4) - $(x-2)^3$ = 0
<=> (x-2)($x^2$ + 2x + 4 -( $x^2$ - 4x + 4)) = 0
<=> (x-2)(6x) = 0
h) $x^3$ + 5$x^2$ -4x -20 = 0
<=> $x^2$(x+5) - 4(x+5) = 0
<=> ($x^2$ -4)(x+5) = 0
<=>(x-2)(x+2)(x+5) = 0
i) $x^3$ - 4$x^2$ + 4x = 0
<=> x($x^2$ - 4x +4) = 0
<=> x$(x-2)^2$ = 0$
j) $x^2$ - 25 + 2(x+5) = 0
<=> (x-5)(x+5) + 2(x+5) = 0
<=> (x+5)(x-3)= 0$
k) 2( $x^2$ + 8x + 16) +x + 4 = 0
<=> 2$(x+4)^2$ + x + 4 = 0
l) $x^2$(x-2) + 7x =14
<=> $x^2$(x-2) + 7(x-2) =0
<=>($x^2$ + 7)(x-2) = 0