Toán Lớp 8: a/ x(x-3)+7(x-3)=0 b 5(x-7)=0 c/ x^3-9x^2+18x=0 Bài2 a/ x^3-4x^2-4x b/ x^2-25 c/ x^3+5x^2+6x

Question

Toán Lớp 8:  a/ x(x-3)+7(x-3)=0 b 5(x-7)=0 c/ x^3-9x^2+18x=0 Bài2 a/ x^3-4x^2-4x b/ x^2-25 c/ x^3+5x^2+6x

kimoanh34 · Answer

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daithanh · Answer

Giải đáp:     1,   a, x.(x - 3) + 7.(x - 3) = 0   &harr; (x - 3).(x + 7) = 0   &harr;  $ left[ begin{matrix} x - 3 = 0   x + 7 = 0 end{matrix} right.$   &harr;  $ left[ begin{matrix} x = 3   x = -7 end{matrix} right.$   Vậy x &isin; {3; -7}   b, 5.(x - 7) = 0   &harr; x - 7 = 0   &harr; x = 0 + 7   &harr; x = 7   Vậy x = 7   c, x^3 - 9x^2 + 18x = 0   &harr; x.(x^2 - 9x + 18) = 0   &harr; x.(x^2 - 6x - 3x + 18) = 0   &harr; x.[x.(x - 6) - 3.(x - 6)] = 0   &harr; x.(x - 6).(x - 3) = 0   &harr;  $ left[ begin{matrix}x = 0   x - 3 = 0   x - 6 = 0 end{matrix} right.$   &harr;  $ left[ begin{matrix}x = 0   x = 3   x = 6 end{matrix} right.$   Vậy x &isin; {0; 3; 6}   ------------------------------   2,   a, x^3 - 4x^2 - 4x   = x.(x^2 - 4x - 4)   b, x^2 - 25   = x^2 - 5^2   = (x - 5).(x + 5)   c, x^3 + 5x^2 + 6x   = x.(x^2 + 5x + 6)   = x.(x^2 + 2x + 3x + 6)   = x.[x.(x + 2) + 3.(x + 2)]   = x.(x + 2).(x + 3)   #dariana