Tìm (x) biết:
Giải thích
a) \[{x^3} + 9{x^2} + 27x + 27 = 0\]
\[{x^3} + 3\,.\,{x^2}\,.\,3 + 3\,.\,x\,.\,{3^2} + {3^3} = 0\]
\({\left( {x + 3} \right)^3} = 0\)
\(x + 3 = 0\)
\(x = - 3\)
Vậy \(x = - 3\)
b) \[9{\left( {x - 1} \right)^2} - \left( {3x + 1} \right)\left( {3x - 1} \right) = 1\]
\[9\left( {{x^2} - 2x + 1} \right) - \left( {9{x^2} - 1} \right) = 1\]
\[9{x^2} - 18x + 9 - 9{x^2} + 1 = 1\]
\[ - 18x + 10 = 1\]
\[18x = 9\]
\(x = \frac{1}{2}\)
Vậy \(x = \frac{1}{2}\).