Question

Tìm x, biết :

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

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

Answer 1

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.............................

Answer 2

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 )

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

\(\Leftrightarrow x^3-1-x^3+3x=15\)

\(\Leftrightarrow3x=16\)

\(\Leftrightarrow x=\dfrac{16}{3}\)