Applicare la formula: $\frac{a}{a}$$=1$, dove $a=x^2$ e $a/a=\frac{21x^2y^3}{7x^2y^2}$

Applicare la formula: $\frac{a^m}{a^n}$$=a^{\left(m-n\right)}$, dove $a^n=y^2$, $a^m=y^3$, $a=y$, $a^m/a^n=\frac{21y^3}{7y^2}$, $m=3$ e $n=2$

Applicare la formula: $\frac{ab}{c}$$=\frac{a}{c}b$, dove $ab=21y$, $a=21$, $b=y$, $c=7$ e $ab/c=\frac{21y}{7}$