b: Ta có: \(\sqrt{28-6\sqrt{3}}-\sqrt{28+6\sqrt{3}}\)
\(=3\sqrt{3}-1-3\sqrt{3}-1\)
=-2
c: Ta có: \(\sqrt{21-12\sqrt{3}}-\sqrt{21+12\sqrt{3}}\)
\(=2\sqrt{3}-3-2\sqrt{3}-3\)
=-6
d: Ta có: \(\sqrt{29+12\sqrt{5}}-\sqrt{29-12\sqrt{5}}\)
\(=2\sqrt{5}+3-2\sqrt{5}+3\)
=6
a) \(\sqrt{9+4\sqrt{2}}+\sqrt{9-4\sqrt{2}}\\ =\sqrt{9+2\sqrt{8}}+\sqrt{9-2\sqrt{8}}\\ =\sqrt{8+2\sqrt{8}.1+1}+\sqrt{8-2\sqrt{8}.1+1}\\ =\sqrt{\left(\sqrt{8}+1\right)^2}+\sqrt{\left(\sqrt{8}-1\right)^2}\\ =\sqrt{8}+1+\sqrt{8}-1\\ =2\sqrt{8}\)
b) Tương tự câu a
\(\sqrt{28-6\sqrt{3}}-\sqrt{28+6\sqrt{3}}\\ =\sqrt{27}-1-\sqrt{27}-1\\ =-2\)
c) \(\sqrt{21-12\sqrt{3}}-\sqrt{21+12\sqrt{3}}\\ \\ =\sqrt{12}-\sqrt{9}-\sqrt{12}-\sqrt{9}\\ =-2\sqrt{9}\\ =-2.3\\ =-6\)
d) \(\sqrt{29+12\sqrt{5}}-\sqrt{29-12\sqrt{5}}\\ =\sqrt{20}+\sqrt{9}-\sqrt{20}+\sqrt{9}\\ =2\sqrt{9}\\ =6\)
