11) <=> VT=$\frac{(\sqrt{2}-1)^4}{(1+\sqrt{2})^2(\sqrt{2}-1)^4}+\frac{(1+\sqrt{2})^4}{(1-\sqrt{2})^4(1+\sqrt{2})^4}=(1+\sqrt{2})^4+(1-\sqrt{2})^4=(3+2\sqrt{2})^2+(3-2\sqrt{2})^2=17-12\sqrt{2}+17+12\sqrt{2}=34=VP$
12)nhân 4 cả tử và mẫu
VT=[tex]\frac{4+2\sqrt{3}}{4+2\sqrt{4+2\sqrt{3}}}+\frac{4-2\sqrt{3}}{4-2\sqrt{4-2\sqrt{3}}}=\frac{(1+\sqrt{3})^2}{4+2\sqrt{(1+\sqrt{3})^2}}+\frac{(1-\sqrt{3})^2}{4-2\sqrt{(\sqrt{3}-1)^2}}=\frac{(1+\sqrt{3})^2}{6+2\sqrt{3}}+\frac{(1-\sqrt{3})^2}{6-2\sqrt{3}}=\frac{1+\sqrt{3}}{2\sqrt{3}}+\frac{\sqrt{3}-1}{2\sqrt{3}}=1=VP[/tex]