a) \(\left(x-2\right)\left(x^2+2x+4\right)\) (sửa đề)
\(=\left(x-2\right)\left(x^2+x.2+2^2\right)\)
\(=x^3-2^3=x^3-8\)
b) \(\left(2x+1\right)\left(4x^2-2x+1\right)\) (sửa đề)
\(=\left(2x+1\right)\left[\left(2x\right)^2-2x.1+1^2\right]\)
\(=\left(2x\right)^3+1^3=8x^3+1\)
c) \(\left(1-\dfrac{x}{2}\right)\left(1+\dfrac{x}{2}+\dfrac{x^2}{4}\right)\)
\(=\left(1-\dfrac{x}{2}\right)\left[1^2+1.\dfrac{x}{2}+\left(\dfrac{x}{2}\right)^2\right]\)
\(=1^3-\left(\dfrac{x}{2}\right)^3=1-\dfrac{x^3}{8}\)
d) \(\left(y-\dfrac{x}{y}\right)\left(y^2+x+\dfrac{x^2}{y^2}\right)\)
\(=\left(y-\dfrac{x}{y}\right)\left[y^2+y.\dfrac{x}{y}+\left(\dfrac{x}{y}\right)^2\right]\)
\(=y^3-\left(\dfrac{x}{y}\right)^3=y^3-\dfrac{x^3}{y^3}\)
#$\mathtt{Toru}$
