Câu hỏi của ĐoànThùyDuyên

Question

Tìm x, biết :

a) ($x2-5$)(x+2)+5x=$2x^2+17$

b) ($x^2-x+1$)(x+1)$-x^3+3x=15$

Aki Tsuki · Accepted Answer

a/ $\left(x^2-5\right)\left(x+2\right)+5x=2x^2+17$

$\Leftrightarrow x^3+2x^2-5x-10+5x-2x^2=17$

$\Leftrightarrow x^3=17+10=27\Leftrightarrow x=3$

Vậy x = 3

b/ $\left(x^2-x+1\right)\left(x+1\right)-x^3+3x=15$

$\Leftrightarrow x^3+1-x^3+3x=15$

$\Leftrightarrow3x=14\Leftrightarrow x=\dfrac{14}{3}$

Vậy.............................Câu trả lời: a/ $\left(x^2-5\right)\left(x+2\right)+5x=2x^2+17$

$\Leftrightarrow x^3+2x^2-5x-10+5x-2x^2=17$

$\Leftrightarrow x^3=17+10=27\Leftrightarrow x=3$

Vậy x = 3

b/ $\left(x^2-x+1\right)\left(x+1\right)-x^3+3x=15$

$\Leftrightarrow x^3+1-x^3+3x=15$

$\Leftrightarrow3x=14\Leftrightarrow x=\dfrac{14}{3}$

Vậy.............................

DƯƠNG PHAN KHÁNH DƯƠNG · Answer

a )

$\left(2x-5\right)\left(x+2\right)+5x=2x^2+17$

$\Leftrightarrow2x^2-x-10+5x-2x^2-17=0$

$\Leftrightarrow4x-27=0$

$\Leftrightarrow x=\dfrac{27}{4}$

b )

$\left(x^2-x+1\right)\left(x+1\right)-x^3+3x=15$

$\Leftrightarrow x^3-1-x^3+3x=15$

$\Leftrightarrow3x=16$

$\Leftrightarrow x=\dfrac{16}{3}$Câu trả lời: a )