bạn kiểm tra lại biểu thức A đi bạn

Đặt \(a=\sqrt{x^2-6x+19},a\ge0\) ; \(b=\sqrt{x^2-6x+10},b\ge0\)

\(\Rightarrow\begin{cases}a-b=3\\a^2-b^2=9\end{cases}\)  \(\Rightarrow A=a+b=3\)

\(3T=\left(\sqrt{x^2-6x+19}-\sqrt{x^2-6x+10}\right)\left(\sqrt{x^2-6x+19}+\sqrt{x^2-6x+10}\right)\)

\(=x^2-6x+19-\left(x^2-6x+10\right)=9\)

\(\Rightarrow T=3\)

là 12                                                                                                                    (mình đoán thế)

Xét \(\sqrt{x^2-6x+10}=\sqrt{\left(x-3\right)^2+1}\ge1\)

=> B \(\le11\)

Dấu "=" <=> x = 3

Bài 1: 

a: Ta có: \(\sqrt{3x^2}=\sqrt{12}\)

\(\Leftrightarrow3x^2=12\)

\(\Leftrightarrow x^2=4\)

hay \(x\in\left\{2;-2\right\}\)

b: Ta có: \(\sqrt{\left(x-2\right)^2}=3\)

\(\Leftrightarrow\left[{}\begin{matrix}x-2=3\\x-2=-3\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=5\\x=-1\end{matrix}\right.\)

\(A=\sqrt{x^2-6x+9}-\sqrt{x^2+6x+9}\)

\(A=\sqrt{x^2-6x+3^2}-\sqrt{x^2+6x+3^2}\)

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

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

\(TH1:x-3>=0\)

\(< =>x+3>=0\)

\(\left|x-3\right|-\left|x+3\right|=1\)

\(x-3-x-3=1\)

\(-6=1\)(loại)

\(TH2:x-3< =0\)

\(x+3>=0\)

\(< =>\left|x-3\right|-\left|x+3\right|=1\)

\(3-x-x-3\)

\(-2x=1\)

\(x=-\frac{1}{2}\left(TM\right)\)

\(TH3:x-3< =0\)

\(x+3< =0\)

\(< =>\left|x-3\right|-\left|x+3\right|=1\)

\(3-x+X+3=1\)

\(6=1\)(loại)

\(< =>x=\left\{\frac{1}{2}\right\}\)để \(A=1\)

\(1,ĐK:x\ne0;x\ne\pm6\)

\(A=\left[\frac{6x+1}{x\left(x-6\right)}+\frac{6x-1}{x\left(x+6\right)}\right].\frac{\left(x+6\right)\left(x-6\right)}{12\left(x^2+1\right)}\)

\(=\frac{6x^2+36x+x+6+6x^2-36x-x+6}{x}.\frac{1}{12\left(x^2+1\right)}\)

\(=\frac{12\left(x^2+1\right)}{x}.\frac{1}{12\left(x^2+1\right)}=\frac{1}{x}\)

\(2,A=\frac{1}{x}=\frac{1}{\frac{1}{\sqrt{9+4\sqrt{5}}}}=\sqrt{9+4\sqrt{5}}\)

Cho tam giác ABC vuông tại B có góc B₁=B₂  ; Â=60^o, kẻ BH vuông góc với AC (H thuộc AC). Qua B kẻ đường thẳng d song song với AC.

a) Tính góc ABH.

b) Chứng minh đường thẳng d vuông góc với BH.

Ta có: \(x=\sqrt{\dfrac{2}{3}}:\sqrt{\dfrac{3}{2}}\)

\(=\sqrt{\dfrac{2}{3}:\dfrac{3}{2}}=\sqrt{\dfrac{2}{3}\cdot\dfrac{2}{3}}=\dfrac{2}{3}\)

Ta có: \(M=\sqrt{6x+5}\)

\(=\sqrt{6\cdot\dfrac{2}{3}+5}=\sqrt{9}=3\)

Ta có  \(x=\sqrt{\dfrac{2}{3}}:\sqrt{\dfrac{3}{2}}=\sqrt{\dfrac{2}{3}.\dfrac{2}{3}}=\dfrac{2}{3}\)

Thay \(x=\dfrac{2}{3}\) vào biếu thức \(M\), ta được :

\(M=\sqrt{6.\dfrac{2}{3}+5}=\sqrt{4+5}=\sqrt{9}=3\)

\(x=\sqrt{\dfrac{2}{3}}:\sqrt{\dfrac{3}{2}}=\sqrt{\dfrac{2}{3}\cdot\dfrac{2}{3}}=\dfrac{2}{3}\)

\(M=\sqrt{6\cdot\dfrac{2}{3}+5}=\sqrt{9}=3\)