Question

1)7x^2-49x
2)8x^2-16x
3)2x^3+40x
4)-x^3+16x

Answer 1

1)

`7x^2 -49x=0`

`<=>x(7x-49)=0`

\(< =>\left[{}\begin{matrix}x=0\\7x-49=0\end{matrix}\right.\\ < =>\left[{}\begin{matrix}x=0\\x=7\end{matrix}\right.\)

2)

`8x^2 -16x=0`

`<=>x(8x-16)=0`

\(< =>\left[{}\begin{matrix}x=0\\8x-16=0\end{matrix}\right.\\ < =>\left[{}\begin{matrix}x=0\\x=2\end{matrix}\right.\)

3)

`2x^3 +40x=0`

`<=>x(2x^2 +40)=0`

`<=>x=0` hoặc`2x^2 +40=0`

`<=>x=0` hoặc `2x^2 =-40` (vô lí vì `2x^2` luôn lớn hơn hoặc bằng 0)

`<=>x=0`

 

4)

`-x^3 +16x=0`

`<=>x^3 -16x=0`

`<=>x(x^2 -16)=0`

\(< =>\left[{}\begin{matrix}x=0\\x^2-16=0\end{matrix}\right.\\ < =>\left[{}\begin{matrix}x=0\\x^2=16\end{matrix}\right.\\ < =>\left[{}\begin{matrix}x=0\\x=4\\x=-4\end{matrix}\right.\)