Đáp án+ Giải thích các bước giải:
1) $75x^3=3x$
⇔$75x^3-3x=0$
⇔$3x(25x^2-1)=0$
⇔$3x(25x^2-1)=0$
⇔$\left[\begin{matrix} 3x=0\\ 25x^2-1=0\end{matrix}\right.$
⇔$\left[\begin{matrix} x=0\\ x^2=1/25\end{matrix}\right.$
⇔$\left[\begin{matrix} x=0\\ x=\pm1/5\end{matrix}\right.$
2) $3x(2x-5)-(2x-3)(1+3x)=7$
⇔$6x^2-15x-2x-6x^2+ 3+ 9x-7=0$
⇔$-8x=4$
⇔$x=-0,5$
3) $x^2(2x-1)+2=4x$
⇔$x^2(2x-1)+2-4x=0$
⇔$x^2(2x-1)+2(1-2x)=0$
⇔$x^2(2x-1)-2(2x-1)=0$
⇔$(x^2-2)(2x-1)=0$
⇔$\left[\begin{matrix} x^2-2=0\\ 2x-1=0\end{matrix}\right.$
⇔$\left[\begin{matrix} x=\pm\sqrt{2} \\ x=1/2\end{matrix}\right.$
4) $2x^2-8=15x$
⇔$2x^2-15x-8=0$
⇔$2x^2+x-16x-8=0$
⇔$x(2x+1)-8(2x+1)=0$
⇔$(x-8)(2x+1)=0$
⇔$\left[\begin{matrix} x=8\\ x=-1/2\end{matrix}\right.$
