\(\frac{2}{5}x\left(y-1\right)-\frac{2}{5}y\left(y-1\right)\)
\(=\left(y-1\right)\left[\left(\frac{2}{5}x-\frac{2}{5}y\right)\right]\)
\(=\left(y-1\right)\frac{2}{5}\left(x-y\right)\)
\(\frac{1}{25}x^2-64y^2\)
\(=\left(\frac{1}{5}x\right)^2-8^2\)
\(=\left(\frac{1}{5}x+8\right)\left(\frac{1}{5}x-8\right)\)
\(x^3+\frac{1}{27}=x^3+\left(\frac{1}{3}\right)^3\)
\(=\left(x+\frac{1}{3}\right)\left(x^2-\frac{1}{3}x+\frac{1}{9}\right)\)
\(8x^3+12x^2y+6xy+y^3\)
\(=2^3+3.4x^2y+3.2x.y^2+y^3\)
\(=\left(2+y\right)^3\)