Question

Tìm x

a) 49 - ( 3x - 1 )² = 0

b) ( x - 1 )³ - ( x + 2 )( x² - 2x + 4 ) = 3 ( 1 - x² )

Mọi người nhớ giải thích ra giùm mình nhé!

Answer 1

a) \(49-\left(3x-1\right)^2=0\)

\(\Leftrightarrow7^2-\left(3x-1\right)^2=0\)

\(\Leftrightarrow\left(7-3x+1\right)\left(7+3x-1\right)=0\)

\(\Leftrightarrow\left(8-3x\right)\left(6+3x\right)=0\)

\(\hept{\begin{cases}8-3x=0\\6+3x=0\end{cases}}\Rightarrow\hept{\begin{cases}x=\frac{8}{3}\\x=-2\end{cases}}\)

Vậy \(x=\frac{8}{3};x=-2\)

b) \(\left(x-1\right)^3-\left(x+2\right)\left(x^2-2x+4\right)=3\left(1-x^2\right)\)

\(\Leftrightarrow\left(x-1\right)^3-\left(x^3+2^3\right)-3\left(1-x^2\right)=0\)

\(\Leftrightarrow x^3-3x^2+3x-1-x^3-8-3+3x^2=0\)

\(\Leftrightarrow3x-12=0\)

\(\Rightarrow x=4\)

Vậy \(x=4\)