Bài 2
1) $\sqrt[]{9-2\sqrt[]{14}}$
=$\sqrt[]{(\sqrt[]{7})^2-2.\sqrt[]{7}.\sqrt[]{2}+(\sqrt[]{2})^2}$
=$\sqrt[]{(\sqrt[]{7}-\sqrt[]{2})^2}$
=|$\sqrt[]{7}-$ $\sqrt[]{2}$|
= $\sqrt[]{7}$-$\sqrt[]{2}$(vì $\sqrt[]{7}$-$\sqrt[]{2}$ > 0)
2)$\sqrt[]{29-4\sqrt[]{7}}$
= $\sqrt[]{(2\sqrt[]{7})^2-2.2\sqrt[]{7}.1+1^2}$
=$\sqrt[]{(2\sqrt[]{7}-1)^2}$=|$2\sqrt[]{7}-1$|
=$2\sqrt[]{7}-1$(vì $2\sqrt[]{7}-1$>0)
3)$\sqrt[]{9-4\sqrt[]{5}}$
=$\sqrt[]{2^2-2.2.\sqrt[]{5}+(\sqrt[]{5})^2}$
= $\sqrt[]{(2-\sqrt[]{5})^2}$
=|$2-\sqrt[]{5}$|
= $\sqrt[]{5}-2$ (vì $\sqrt[]{5}-2>0)$
4) $\sqrt[]{17-12\sqrt[]{2}}$ + $\sqrt[]{17+12\sqrt[]{2}}$
=$\sqrt[]{(2\sqrt[]{2})^2-2.2\sqrt[]{2}.3+3^2}$+$\sqrt[]{(2\sqrt[]{2})^2+2.2\sqrt[]{2}.3+3^2}$
= $\sqrt[]{(2\sqrt[]{2}-3)^2}$+ $\sqrt[]{(2\sqrt[]{2}+3)^2}$
=|$2\sqrt[]{2}-3$|+|$2\sqrt[]{2}+3$|
= $3-2\sqrt[]{2}$+$2\sqrt[]{2}+3$ (vì $3-2\sqrt[]{2}$>0)
=9
câu 5,6 mai mik mới lm đc giờ mik có vc bận r nha
