Câu hỏi của Lililala

Question

Bài 1 : Tìm x :

a, $x^2-2x=24$

b, $\left(x-3\right)\left(x^2+3x+9\right)+x\left(x+2\right)\left(2-x\right)$ $=1$

Trúc Giang · Accepted Answer

a) $x^2-2x=24$

$\Rightarrow x^2-2x-24=0$

$\Rightarrow x^2-2x+1-25=0$

$\Rightarrow\left(x-1\right)^2-25=0$

$\Rightarrow\left(x-1\right)^2=0+25=25=\left(\pm5\right)^2$

$\Rightarrow\left[{}\begin{matrix}x-1=5\x-1=-5\end{matrix}\right.$

$\Rightarrow\left[{}\begin{matrix}x=5+1=6\x=-5+1=-4\end{matrix}\right.$

b) $\left(x-3\right)\left(x^2+3x+9\right)+x\left(x+2\right)\left(2-x\right)=1$

$\Rightarrow\left(x^3-3^3\right)+x\left(2+x\right)\left(2-x\right)=1$

$\Rightarrow\left(x^3-27\right)+x\left(2^2-x^2\right)=1$

$\Rightarrow x^3-27+4x-x^3=1$

$\Rightarrow4x=1+27=28$

$\Rightarrow x=28:4=7$

P/s: Ko chắc!Câu trả lời: a) $x^2-2x=24$