Applicare la formula: $\frac{a}{b}c$$=\frac{ca}{b}$, dove $a=1$, $b=3$, $c=\sqrt{21}$, $a/b=\frac{1}{3}$ e $ca/b=\frac{1}{3}\sqrt{21}$

Applicare la formula: $\frac{a}{b}c$$=\frac{ca}{b}$, dove $a=-2$, $b=3$, $c=\sqrt{3}$, $a/b=-\frac{2}{3}$ e $ca/b=-\frac{2}{3}\sqrt{3}\sqrt{7}x$

Applicare la formula: $1x$$=x$, dove $x=\sqrt{21}$

Applicare la formula: $a\frac{b}{c}$$=\frac{ba}{c}$, dove $a=\sqrt{7}x$, $b=-2\sqrt{3}$ e $c=3$

Applicare la formula: $\frac{a}{b}+\frac{c}{b}$$=\frac{a+c}{b}$, dove $a=\sqrt{21}$, $b=3$ e $c=-2\sqrt{3}\sqrt{7}x$