[tex]\displaystyle\bf\\7\sqrt{3}=\sqrt{a}\\\\\sqrt{a}=7\sqrt{3}~~\Big|~Ridicam~la~patrat.\\\\\Big(\sqrt{a}\Big)^2=\Big(7\sqrt{3}\Big)^2\\\\a=49\times3\\\\\boxed{\bf a=147}\\\\\\3\sqrt{7}=\sqrt{b}\\\\\sqrt{b}=3\sqrt{7}~~\Big|~Ridicam~la~patrat.\\\\b=9\times7\\\\\boxed{\bf b=63}\\\\\\a-b=147-63\\\\\boxed{\boxed{\bf a-b=84}}\\\\[/tex]
