Question

x^3+27=9-x^2

Answer 1

x^3 +3^3=3^2 -x^2

Answer 2

\(X^3+27=9-x^2\)

\((X+3)(x^2-3x+9)- (9-x^2)=0\)

\((X+3)(x^2-3x+9)-(x+3)(3-x)=0\)

\((X+3)(x^2-3x+9-3+x)=0\)

\((X+3)(x^2-2x+6)=0\)

th1 x+3=0 

          X=-3

Th2 \(X^2-2x+6=0\)

     \((X^2-2x+4)+2=0\)

    \((X-2)^2+2=0\)
ta có \((X-2)^2> hoặc = 0\)

  Mà 2>0. Suy ra \((X-2)^2+2>0 ( vô nghiệm)\)

suy ra x=-3

Answer 3

\(x^3+27=9-x^2\Leftrightarrow x^3+x^2+18=0\Leftrightarrow\left(x+3\right)\left(x^2-2x+6\right)\Leftrightarrow x+3=0\Leftrightarrow x=-3\)(do \(x^2-2x+6=\left(x-1\right)^2+5\ge5>0\))