\(\sqrt{4}+\sqrt{15}-\sqrt{4}-\sqrt{15}-\sqrt{2}-\sqrt{3}\)

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

cvfbhm,

Xin lỗi em ko biết làm , em vẫn chưa lên lớp 9

1)\(\left(\frac{1}{a-\sqrt{a}}+\frac{1}{\sqrt{a}-1}\right):\frac{\sqrt{a}+1}{a-2\sqrt{a}+1}\)

\(=\left(\frac{1}{\sqrt{a}\left(\sqrt{a}-1\right)}+\frac{\sqrt{a}}{\sqrt{a}\left(\sqrt{a}-1\right)}\right)\cdot\frac{\left(\sqrt{a}-1\right)^2}{\sqrt{a}+1}\)

\(=\frac{\sqrt{a}+1}{\sqrt{a}\left(\sqrt{a}-1\right)}\cdot\frac{\left(\sqrt{a}-1\right)^2}{\sqrt{a}+1}\)

\(=\frac{\sqrt{a}-1}{\sqrt{a}}\)

Bằng không!

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

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

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

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

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

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

\(\sqrt{5}-17\sqrt{3}\)

\(4\sqrt{12}-3\sqrt{45}-5\sqrt{75}+2\sqrt{125}\\ =8\sqrt{3}-9\sqrt{5}-25\sqrt{3}+10\sqrt{5}\\ \sqrt{5}-17\sqrt{3}\)

\(\frac{1}{3}-\sqrt{7}-\frac{1}{3}+\sqrt{7}=0\)

\(\sqrt{12}-2\sqrt{48}+\frac{7}{5}\sqrt{75}\)

=\(2\sqrt{3}-8\sqrt{3}+7\sqrt{3}\)

\(\sqrt{3}\)

Đề bài yêu cầu gì?

\(2\sqrt{18}-7\sqrt{2}+\sqrt{162}\)

\(=2.3\sqrt{2}-7\sqrt{2}+9\sqrt{2}\)

\(=6\sqrt{2}-7\sqrt{2}+9\sqrt{2}\)

\(=\left(6-7+9\right).\sqrt{2}\)

\(=8\sqrt{2}\)

Chúc bạn hok tốt!!!Vũ Quỳnh Nhung

ý bạn là \(2\sqrt{18-7\sqrt{2}+\sqrt{162}}\) hay \(2\sqrt{18}-7\sqrt{2}+\sqrt{162}\)