Lời giải:
a.
$\sqrt{13-2\sqrt{12}}+\sqrt{12}=\sqrt{12-2\sqrt{12}+1}+\sqrt{12}$
$=\sqrt{(\sqrt{12}-1)^2}+\sqrt{12}$
$=|\sqrt{12}-1|+\sqrt{12}=\sqrt{12}-1+\sqrt{12}=2\sqrt{12}-1$
b.
$\sqrt{8-2\sqrt{12}}-\sqrt{6}$
$=\sqrt{6-2\sqrt{2.6}+2}-\sqrt{6}$
$=\sqrt{(\sqrt{6}-\sqrt{2})^2}-\sqrt{6}$
$=|\sqrt{6}-\sqrt{2}|-\sqrt{6}=\sqrt{6}-\sqrt{2}-\sqrt{6}=-\sqrt{2}$
c.
$\sqrt{7-2\sqrt{12}}+\sqrt{3}=\sqrt{4-2\sqrt{4.3}+3}+\sqrt{3}$
$=\sqrt{(\sqrt{4}-\sqrt{3})^2}+\sqrt{3}$
$|\sqrt{4}-\sqrt{3}|+\sqrt{3}=\sqrt{4}-\sqrt{3}+\sqrt{3}=\sqrt{4}=2$