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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 8: x^2+12x+36=0 81x^2-625=0 x^3+6x^2+12x+8=0

Toán Lớp 8: x^2+12x+36=0
81x^2-625=0
x^3+6x^2+12x+8=0

Comments ( 2 )

  1. a) x² + 12x + 36 = 0
    ⇔ x² + 2.x.6 + 6² =0
    ⇔ (x + 6)² =0
    ⇔ x + 6 = 0
    ⇔ x = -6
    b) 81.x² – 625 =0
    ⇔ 81.x² = 625
    ⇔ x² = $\frac{625}{81}$ 
    ⇔ \(\left[ \begin{array}{l}x=\sqrt{\frac{625}{81}}= \frac{25}{9} \\x=-\sqrt{\frac{625}{81}}= -\frac{25}{9}\end{array} \right.\) 
    c) x³ + 6.x² + 12x + 8 = 0
    ⇔ (6.x² + 12x) + (x³ + 8) = 0
    ⇔ 6x(x + 2) + (x + 2).(x² – 2x + 4) = 0
    ⇔ (x + 2).(x² – 2x + 6x + 4 ) = 0
    ⇔ (x + 2).(x² + 4x +4) =0
    ⇔ (x + 2).(x + 2)² = 0
    ⇔ (x + 2)³ = 0
    ⇔ x + 2 = 0
    ⇔ x = -2
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  2. $x^2+12x+36=0$
    $⇔(x+6)^2=0$
    $⇔x+6=0$
    $⇔x=-6$
    Vậy $S=\{6\}$
    $81x^2-625=0$
    $⇔(9x-25)(9x+25)=0$
    $⇔$\(\left[ \begin{array}{l}x=\dfrac{25}{9}\\x=-\dfrac{25}{9}\end{array} \right.\) 
    Vậy $S=\{±\dfrac{25}{9}\}$
    $x^3+6x^2+12x+8=0$
    $⇔(x+2)(x^2-2x+4)+6x(x+2)=0$
    $⇔(x+2)(x^2+4x+4)=0$
    $⇔(x+2)(x+2)^2=0$
    $⇔(x+2)^3=0$
    $⇔x+2=0$
    $⇔x=-2$
    Vậy $S=\{-2\}$

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222-9+11+12:2*14+14 = ? ( )

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