$ a$,$A$=($2$$-$$\sqrt{3}$ )($2$$+$$\sqrt{3}$)
$=$$4$$-$$3$
$=$$1$
$b$,$A$$=$$x$$-$$4$
$=$($\sqrt{x}$ $-$$2$)($\sqrt{x}$ $+$$2$)
$B$$=$$x$$+$$\sqrt{x}$ $-$$2$
$=$$x$$+$$2$$\sqrt{x}$ $-$$\sqrt{x}$$-2$
$=$$\sqrt{x}$ ($\sqrt{x}$$-2$)$+($$\sqrt{x}$$-2$)
$=$($\sqrt{x}$ $-2$)($\sqrt{x}$$+1$)