Question

Answer 1

b: \(\left(x+5\right)x^2=81\left(x+5\right)\)

\(\Leftrightarrow\left(x+5\right)\left(x+9\right)\left(x-9\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=-5\\x=9\\x=-9\end{matrix}\right.\)

Answer 2

a) \(\Rightarrow12x-3x^2+2x+3x^2=18-4x\)

\(\Rightarrow18x=18\Rightarrow x=1\)

b) \(\Rightarrow x^3+5x^2=81x+405\Rightarrow x^3+5x^2-81x-405=0\)

\(\Rightarrow\left(x-9\right)\left(x+5\right)\left(x+9\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}x=9\\x=-5\\x=-9\end{matrix}\right.\)