Khai triển các biểu thức sau: ( 3x - 1/3)^5.

Lời giải

\({\left( {3x - \frac{1}{3}} \right)^5} = {\left( {3x} \right)^5} + 5.{\left( {3x} \right)^4}.\left( { - \frac{1}{3}} \right) + 10.{\left( {3x} \right)^3}.{\left( { - \frac{1}{3}} \right)^2}\)

\( + 10.{\left( {3x} \right)^2}.{\left( { - \frac{1}{3}} \right)^3} + 5.\left( {3x} \right).{\left( { - \frac{1}{3}} \right)^4} + {\left( { - \frac{1}{3}} \right)^5}\)

\( = 243{x^5} - 135{x^4} + 30{x^3} - \frac{{10}}{3}{x^2} + \frac{5}{{27}}x - \frac{1}{{243}}\).