Applicare la formula: $\left(a+b\right)^2$$=a^2+2ab+b^2$, dove $a=\frac{2}{5}a^2b$, $b=-\frac{1}{2}a$ e $a+b=\frac{2}{5}a^2b-\frac{1}{2}a$

Applicare la formula: $x\cdot x^n$$=x^{\left(n+1\right)}$, dove $x^nx=\frac{4}{5}\cdot -\frac{1}{2}a^2ba$, $x=a$, $x^n=a^2$ e $n=2$

Applicare la formula: $\left(ab\right)^n$$=a^nb^n$

Applicare la formula: $\frac{a}{b}\frac{c}{f}$$=\frac{ac}{bf}$, dove $a=4$, $b=5$, $c=-1$, $a/b=\frac{4}{5}$, $f=2$, $c/f=-\frac{1}{2}$ e $a/bc/f=\frac{4}{5}\cdot -\frac{1}{2}a^{3}b$