Question

giải phương trình 4x^3 - 4x^2 -15x +18=0

Answer 1

\(\Leftrightarrow4x^3+8x^2-12x^2-24x+9x+18=0\)

\(\Leftrightarrow\left(x+2\right)\left(4x^2-12x+9\right)=0\)

\(\Leftrightarrow\left(x+2\right)\left(2x-3\right)^2=0\)

=>x=3/2 hoặc x=-2

Answer 2

4x^3-4x^2-15x+18=0 

<=> 4x^3 +8x^2-12x^2-24x+9x+18=0

<=> 4x^2(x+2)-12x(x+2)+9(x+2)=0

<=> (x+2).(4x^2-12x+9)=0

<=> (x+2).(2x-3)^2=0

<=> x+2=0

       (2x-3)^2=0

<=> x=-2 

       x=3/2