2:

a: =(1+căn 3)^2-5

=4+2căn 3-5

=2căn 3-1

b: \(=\sqrt{\dfrac{125}{7}\cdot\dfrac{35}{81}}=\sqrt{\dfrac{625}{81}}=\dfrac{25}{9}\)

c: \(=\left(\sqrt{3}-1\right)\left(\sqrt{3}+1\right)-\sqrt{6}+\sqrt{2}\)

=2-căn 6+căn 2

3:

a: \(=\dfrac{2\sqrt{3}+3\sqrt{3}-\sqrt{3}}{\sqrt{3}}=2+3-1=5\)

b: \(=\dfrac{6\sqrt{2}+7\sqrt{2}-5\sqrt{2}}{\sqrt{2}}=13-5=8\)

c: \(=\dfrac{12-10+8}{2}=5\)

d: \(=\sqrt{\dfrac{1}{5}:5}-\sqrt{\dfrac{9}{5}:5}+\sqrt{5:5}\)

=1/5-3/5+1

=3/5

Bài 3: 

1: Ta có: \(P=\dfrac{\sqrt{x}+1}{\sqrt{x}-2}+\dfrac{2\sqrt{x}}{\sqrt{x}+2}-\dfrac{5\sqrt{x}+2}{x-4}\)

\(=\dfrac{x+3\sqrt{x}+2+2x-4\sqrt{x}-5\sqrt{x}-2}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+2\right)}\)

\(=\dfrac{\sqrt{x}}{\sqrt{x}+2}\)

Tách ra đi bạn ơi, dài quá

Lời giải:

a. ĐKXĐ: $x>0; x\neq 4$

b.

\(M=\sqrt{x}.\left[\frac{1}{\sqrt{x}-2}+\frac{1}{\sqrt{x}+2}\right].\frac{x-4}{2\sqrt{x}}\)

\(=\frac{2\sqrt{x}}{(\sqrt{x}-2)(\sqrt{x}+2)}.\frac{x-4}{2}=\frac{2\sqrt{x}}{x-4}.\frac{x-4}{2}=\sqrt{x}\)

c. Để $M>3\Leftrightarrow \sqrt{x}>3\Leftrightarrow x>9$

Kết hợp đkxđ suy ra $x>9$ thì $M>3$

\(a,=2\sqrt{2}\left(\sqrt{5}-1\right)\sqrt{4+\sqrt{\left(\sqrt{5}-1\right)^2}}\\ =2\sqrt{2}\left(\sqrt{5}-1\right)\sqrt{4+\sqrt{5}-1}\\ =2\left(\sqrt{5}-1\right)\sqrt{6-2\sqrt{5}}\\ =2\left(\sqrt{5}-1\right)\sqrt{\left(\sqrt{5}-1\right)^2}\\ =2\left(\sqrt{5}-1\right)^2=2\left(6-2\sqrt{5}\right)=12-4\sqrt{5}\\ b,=\left(4+\sqrt{15}\right)\left(\sqrt{5}-\sqrt{3}\right)\sqrt{8-2\sqrt{15}}\\ =\left(4+\sqrt{15}\right)\left(\sqrt{5}-\sqrt{3}\right)\sqrt{\left(\sqrt{5}-\sqrt{3}\right)^2}\\ =\left(4+\sqrt{15}\right)\left(\sqrt{5}-\sqrt{3}\right)^2\\ =\left(4+\sqrt{15}\right)\left(8-2\sqrt{15}\right)\\ =32-8\sqrt{15}+8\sqrt{15}-30=2\)

a.

Ta có: \(\sqrt{x^2+12}>\sqrt{x^2+5}\Rightarrow\sqrt{x^2+12}-\sqrt{x^2+5}>0\)

\(\Rightarrow3x-5=\sqrt{x^2+12}-\sqrt{x^2+5}>0\Rightarrow x>\dfrac{5}{3}\)

Do đó:

\(\sqrt{x^2+12}+5=3x+\sqrt{x^2+5}\)

\(\Leftrightarrow3\left(x-2\right)+\sqrt{x^2+5}-3-\left(\sqrt{x^2+12}-4\right)=0\)

\(\Leftrightarrow3\left(x-2\right)+\dfrac{x^2-4}{\sqrt{x^2+5}+3}-\dfrac{x^2-4}{\sqrt{x^2+12}+4}=0\)

\(\Leftrightarrow\left(x-2\right)\left(3+\dfrac{x+2}{\sqrt{x^2+5}+3}-\dfrac{x+2}{\sqrt{x^2+12}+4}\right)=0\)

\(\Leftrightarrow\left(x-2\right)\left[3+\left(x+2\right)\left(\dfrac{1}{\sqrt{x^2+5}+3}-\dfrac{1}{\sqrt{x^2+12}+4}\right)\right]=0\)

\(\Leftrightarrow\left(x-2\right)\left(3+\dfrac{\left(x+2\right)\left(\sqrt{x^2+12}-\sqrt{x^2+5}+1\right)}{\left(\sqrt{x^2+5}+3\right)\left(\sqrt{x^2+12}+4\right)}\right)=0\)

\(\Leftrightarrow x-2=0\) (do \(x>\dfrac{5}{3}\) nên ngoặc phía sau luôn dương)

\(\Leftrightarrow x=2\)

b.

\(\Delta=\left(m-1\right)^2-4\left(-m^2+m-2\right)=5m^2-6m+9=5\left(m-\dfrac{3}{5}\right)^2+\dfrac{36}{5}>0\)

Phương trình đã cho luôn có 2 nghiệm với mọi m

Theo hệ thức Viet: \(\left\{{}\begin{matrix}x_1+x_2=m-1\\x_1x_2=-m^2+m-2\end{matrix}\right.\)

\(Q=\left(\dfrac{x_1}{x_2}\right)^2+\left(\dfrac{x_2}{x_1}\right)^2+2-2=\left(\dfrac{x_1}{x_2}+\dfrac{x_2}{x_1}\right)^2-2\)

\(=\left(\dfrac{x_1^2+x_2^2}{x_1x_2}\right)^2-2=\left[\dfrac{\left(x_1+x_2\right)^2-2x_1x_2}{x_1x_2}\right]^2-2\)

\(=\left[\dfrac{\left(m-1\right)^2-2\left(-m^2+m-2\right)}{-m^2+m-2}\right]^2-2=\left(\dfrac{3m^2-4m+5}{m^2-m+2}\right)^2-2\)

Ta có: \(\dfrac{3m^2-4m+5}{m^2-m+2}=\dfrac{3\left(m-\dfrac{2}{3}\right)^2+\dfrac{11}{3}}{\left(m-\dfrac{1}{2}\right)^2+\dfrac{7}{4}}>0\)

\(\dfrac{3m^2-4m+5}{m^2-m+2}=\dfrac{21m^2-28m+35}{7\left(m^2-m+2\right)}=\dfrac{22\left(m^2-m+2\right)-\left(m^2+6m+9\right)}{7\left(m^2-m+2\right)}=\dfrac{22}{7}-\dfrac{\left(m+3\right)^2}{7\left(m^2-m+2\right)}\le\dfrac{22}{7}\)

\(\Rightarrow0< \dfrac{3m^2-4m+5}{m^2-m+2}\le\dfrac{22}{7}\)

\(\Rightarrow Q\le\left(\dfrac{22}{7}\right)^2-2\)

Dấu "=" xảy ra khi \(m+3=0\Leftrightarrow m=-3\)