Toán Lớp 8: ìm x. a, 3x(x – 2) +4(x – 2) = 0 b.

Question

Toán Lớp 8:  ìm x.               a, 3x(x – 2) +4(x – 2) = 0               b.

dananhnhu2k4 · Answer

a, 3x(x &ndash; 2) +4(x &ndash; 2) = 0           (x - 2) . (3x + 4) = 0    $ Rightarrow$$ left[ begin{matrix} x-2=0   3x+4=0 end{matrix} right.$    $ Rightarrow$$ left[ begin{matrix} x=2   3x=-4 end{matrix} right.$   $ Rightarrow$$ left[ begin{matrix} x=2   x=-4/3 end{matrix} right.$      Vậy x $ in$ {2; $ frac{-4}{3}$}       b,(x+3).(x+4)-(x-3)(x-5)=2        $ text{$x^{2}$ + 4x + 3x + 12 - ($x^{2}$ - 5x - 3x + 15) - 2 = 0 }$        $ text{$x^{2}$ + 4x + 3x +12 - $x^{2}$ + 5x + 3x - 15 - 2 = 0 }$                                                      $ text{15x - 5 = 0}$                                                      $ text{15x = 5}$                                                     $ text{x = $ frac{1}{3}$ }$       Vậy x = $ frac{1}{3}$

thuminhthong · Answer

a) 3x(x-2)+4(x-2)=0 <=>(3x+4)(x-2)=0 <=> ( left[ begin{array}{l}3x+4=0 x-2=0 end{array} right. ) <=> ( left[ begin{array}{l}3x=-4 x=2 end{array} right. ) <=> ( left[ begin{array}{l}x= dfrac{-4}{3} x=2 end{array} right. ) vậy S={-4/3;2}