Tìm (x) biết: (a),,2{x^2} - 6x = 0,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,b),,(x + 3)({x^2} - 3x + 9) - x({x^2} - 2) = 15)
Giải chi tiết:
(begin{array}{l}a),,2{x^2} - 6x = 0,,,,,,,,,,,,, Leftrightarrow ,2x(x - 3) = 0,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Rightarrow left[ begin{array}{l}2x = 0x - 3 = 0end{array} right.,,,, Rightarrow left[ begin{array}{l}x = 0x = 3end{array} right..end{array})
Vậy (x = 0) hoặc (x = 3) .
(begin{array}{l}b),,(x + 3)({x^2} - 3x + 9) - x({x^2} - 2) = 15,, Leftrightarrow {x^2} + 27 - {x^3} + 2x = 15 Leftrightarrow 2x + 27 = 15 Leftrightarrow 2x = 15 - 27 Leftrightarrow ,2x = - 12 Leftrightarrow ,x = - 12:2 Leftrightarrow x = - 6end{array})
Vậy (x = - 6).