Đáp án:
Giải thích các bước giải:
a) $\sqrt{20}$ $-$ $\sqrt{45}$ $+$ $\sqrt{5}$ $=$ $2\sqrt{5}$ $-$ $3\sqrt{5}$ $+$ $\sqrt{5}$ $=$ $\sqrt{5}(2-3+1)$ $=$ $0$
b) $(1-\frac{7+\sqrt{7}}{1+\sqrt{7}})$$.$$(\frac{7-\sqrt{7}}{1-\sqrt{7}}-1)$ $=$ $\frac{-6}{1+\sqrt{7}}$ $.$ $\frac{6}{1-\sqrt{7}}$ $=$ $\frac{-36}{-6}$ $=$ $6$
c)$\sqrt{3-2\sqrt{2}}$ $+$ $\sqrt{3+2\sqrt{2}}$ $=$ $\sqrt{(\sqrt{2})^{2}-2\sqrt{2}+1}$ $+$ $\sqrt{(\sqrt{2})^{2}+2\sqrt{2}+1}$ $=$ $\sqrt{ (\sqrt{2}-1)^{2}}$ $+$ $\sqrt{ (\sqrt{2}+1)^{2}}$ $=$ $2\sqrt{2}$
