Question

Tìm x:

a) (3x+5)(7-2x)+6x(x+4)=0.

b)x^3-25x=0

 

Answer 1

\(\left(3x+5\right)\left(7-2x\right)+6x\left(x+4\right)=0\)

\(\Leftrightarrow 21x-6x^2+35-10x+6x^2+24x=0\)

\(\Leftrightarrow35x+35=0\)

\(\Leftrightarrow35\left(x+1\right)=0\)

\(\Leftrightarrow x+1=0\)

\(\Leftrightarrow x=-1\)

Answer 2

\(x^3-25x=0\)

\(\Leftrightarrow x\left(x^2-25\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}x=0\\x^2-25=0\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}x=0\\x=\pm5\end{cases}}\)

Vậy ......