Tìm số tự nhiên x, biết : a ) 8x^2 - 5 = 67 b ) ( x + 1 )^3 = 8 c ) ( 4x - 2 )^4 = 16 d ) ( x + 3 )^3 = (2x)^3

Answer.

`a,8x^2-5=67`

`=>8x^2=67+5`

`=>8x^2=72`

`=>x^2=72:8`

`=>x^2=9`

`=>x^2=(+-3)^2`

`=>`\(\left[ \begin{array}{l}x=3\\x=-3\end{array} \right.\) 

Vậy `x=+-3`

`b,(x+1)^3=8`

`=>(x+1)^3=2^3`

`=>x+1=2`

`=>x=2-1`

`=>x=1`

Vậy `x=1`

`c,(4x-2)^4=16`

`=>(4x-2)^4=(+-2)^4`

`=>`\(\left[ \begin{array}{l}4x-2=2\\4x-2=-2\end{array} \right.\) 

`=>`\(\left[ \begin{array}{l}4x=4\\4x=0\end{array} \right.\) 

`=>`\(\left[ \begin{array}{l}x=1\\x=0\end{array} \right.\) 

Vậy `x=1;x=0`

`d,(x+3)^3=(2x)^3`

`=>x+3=2x`

`=>2x-x=3`

`=>x=3`

Vậy `x=3`