Question

[Đào Phúc Việt]

Tìm x biết:

d) (x-2)³-(x-3).(x²+3x+9)+6.(x+1)²=15

e) (x-1)³+(2-x).(4+2x+x²)+3x.(x+2)=17

f) (3x+3)²-18x=36+(x-3).(x²+3x+9)

Giải chi tiết giúp mình nha.Cảm ơn.

Answer 1

[Nguyễn Hoàng Minh]

\(d,\Leftrightarrow x^3-6x^2+12x-8-x^3+27+6x^2+12x+6=15\\ \Leftrightarrow24x=-10\Leftrightarrow x=-\dfrac{5}{12}\\ e,\Leftrightarrow x^3-3x^2+3x-1+8-x^3+3x^2+6x=17\\ \Leftrightarrow9x=10\Leftrightarrow x=\dfrac{10}{9}\\ f,\Leftrightarrow9x^2+18x+9-18x=36+x^3-27\\ \Leftrightarrow x^3-9x^2=0\Leftrightarrow x^2\left(x-9\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=0\\x=9\end{matrix}\right.\)