Question

Rút gọn các biểu thức :

\(a,\sqrt{4+2\sqrt{3}}-\sqrt{4-2\sqrt{3}}\)

b, \(\sqrt{9-4\sqrt{5}}-\sqrt{9+4\sqrt{5}}\)

Answer 1

a) \(\sqrt{4+2\sqrt{3}}-\sqrt{4-2\sqrt{3}}\)

\(=\sqrt{3}+1-\left(\sqrt{3}-1\right)\)

\(=\sqrt{3}+1-\sqrt{3}+1\)

\(=2\)

b) \(\sqrt{9-4\sqrt{5}}-\sqrt{9+4\sqrt{5}}\)

\(=\sqrt{5}-2-\left(2+\sqrt{5}\right)\)

\(=\sqrt{5}-2-\sqrt{5}-2\)

\(=-4\)

Answer 2

a) \(\sqrt{4+2\sqrt{3}}-\sqrt{4-2\sqrt{3}}\)

\(=\sqrt{3+2\sqrt{3}+1}-\sqrt{3-2\sqrt{3}+1}\)

\(=\sqrt{\left(\sqrt{3}+1\right)^2}-\sqrt{\left(\sqrt{3}-1\right)^2}\)

\(=\sqrt{3}+1-\sqrt{3}+1\)

\(=2\)

b) tương tự

Answer 3

\(\sqrt{4+2\sqrt{3}}-\sqrt{4-2\sqrt{3}}\)

\(=\sqrt{3+2\sqrt{3}+1}-\sqrt{3-2\sqrt{3}+1}\)

\(=\sqrt{\left(\sqrt{3}\right)^2+2\sqrt{3}+1^2}-\sqrt{\left(\sqrt{3}\right)^2-2\sqrt{3}+1^2}\)

\(=\sqrt{\left(\sqrt{3}+1\right)^2}-\sqrt{\left(\sqrt{3}-1\right)^2}\)

\(=\left|\sqrt{3}+1\right|-\left|\sqrt{3}-1\right|\)

\(=\sqrt{3}+1+1-\sqrt{3}=2\)

\(\sqrt{9-4\sqrt{5}}-\sqrt{9+4\sqrt{5}}\)

\(=\sqrt{5-4\sqrt{5}+4}-\sqrt{5+4\sqrt{5}+4}\)

\(=\sqrt{\left(\sqrt{5}\right)^2-2\sqrt{5}\cdot2+2^2}-\sqrt{\left(\sqrt{5}\right)^2+2\sqrt{5}\cdot2+2^2}\)

\(=\sqrt{\left(\sqrt{5}-2\right)^2}-\sqrt{\left(\sqrt{5}+2\right)^2}\)

\(=\left|\sqrt{5}-2\right|-\left|\sqrt{5}+2\right|\)

\(=\sqrt{5}-2-\sqrt{5}-2=-4\)

Answer 4

             Bài làm :

 \(\text{a)}\sqrt{4+2\sqrt{3}}-\sqrt{4-2\sqrt{3}}\)

\(=\sqrt{3}+1-\left(\sqrt{3}-1\right)\)

\(=\sqrt{3}+1-\sqrt{3}+1\)

\(=2\)

 \(\text{b)}\sqrt{9-4\sqrt{5}}-\sqrt{9+4\sqrt{5}}\)

\(=\sqrt{5}-2-\left(2+\sqrt{5}\right)\)

\(=\sqrt{5}-2-\sqrt{5}-2\)

\(=-4\)