Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
a: ĐKXĐ: \(\left\{{}\begin{matrix}x\ge0\\x\ne9\end{matrix}\right.\)
Ta có: \(A=\dfrac{\sqrt{x}}{\sqrt{x}+3}+\dfrac{2\sqrt{x}}{\sqrt{x}-3}-\dfrac{3x+9}{x-9}\)
\(=\dfrac{x-3\sqrt{x}+2x+6\sqrt{x}-3x-9}{\left(\sqrt{x}+3\right)\left(\sqrt{x}-3\right)}\)
\(=\dfrac{3\left(\sqrt{x}-3\right)}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}\)
\(=\dfrac{3}{\sqrt{x}+3}\)
b: Thay x=16 vào A, ta được:
\(A=\dfrac{3}{4+3}=\dfrac{3}{7}\)
a) \(A=\left(\dfrac{x}{x+3}-\dfrac{2}{x-3}+\dfrac{x^2-1}{9-x^2}\right):\left(2-\dfrac{x+5}{x+3}\right)\) (ĐK: \(x\ne\pm3\))
\(A=\left[\dfrac{x\left(x-3\right)}{\left(x+3\right)\left(x-3\right)}-\dfrac{2\left(x+3\right)}{\left(x+3\right)\left(x-3\right)}-\dfrac{x^2-1}{\left(x+3\right)\left(x-3\right)}\right]:\left(2+\dfrac{x+5}{x+3}\right)\)
\(A=\dfrac{x^2-3x-2x-6-x^2+1}{\left(x+3\right)\left(x-3\right)}:\dfrac{2\left(x+3\right)-\left(x+5\right)}{x+3}\)
\(A=\dfrac{-5x-5}{\left(x+3\right)\left(x-3\right)}\cdot\dfrac{x+3}{x+1}\)
\(A=\dfrac{-5\left(x+1\right)\left(x+3\right)}{\left(x+3\right)\left(x-3\right)\left(x+1\right)}\)
\(A=\dfrac{-5}{x-3}\)
b) Ta có: \(\left|x\right|=1\)
TH1: \(\left|x\right|=-x\) với \(x< 0\)
Pt trở thành:
\(-x=1\) (ĐK: \(x< 0\))
\(\Leftrightarrow x=-1\left(tm\right)\)
Thay \(x=-1\) vào A ta có:
\(A=\dfrac{-5}{x-3}=\dfrac{-5}{-1-3}=\dfrac{5}{4}\)
TH2: \(\left|x\right|=x\) với \(x\ge0\)
Pt trở thành:
\(x=1\left(tm\right)\) (ĐK: \(x\ge0\))
Thay \(x=1\) vào A ta có:
\(A=\dfrac{-5}{x-3}=\dfrac{-5}{1-2}=\dfrac{5}{2}\)
c) \(A=\dfrac{1}{2}\) khi:
\(\dfrac{-5}{x-3}=\dfrac{1}{2}\)
\(\Leftrightarrow-10=x-3\)
\(\Leftrightarrow x=-10+3\)
\(\Leftrightarrow x=-7\left(tm\right)\)
d) \(A\) nguyên khi:
\(\dfrac{-5}{x-3}\) nguyên
\(\Rightarrow x-3\inƯ\left(-5\right)\)
\(\Rightarrow x\in\left\{8;-2;2;4\right\}\)
a: \(A=\left(\dfrac{x}{x+3}-\dfrac{2}{x-3}+\dfrac{x^2-1}{9-x^2}\right):\left(2-\dfrac{x+5}{x+3}\right)\)
\(=\dfrac{x\left(x-3\right)-2\left(x+3\right)-x^2+1}{\left(x-3\right)\left(x+3\right)}:\dfrac{2x+6-x-5}{x+3}\)
\(=\dfrac{x^2-3x-2x-6-x^2+1}{\left(x-3\right)\left(x+3\right)}\cdot\dfrac{x+3}{x+1}\)
\(=\dfrac{-5x-5}{\left(x-3\right)}\cdot\dfrac{1}{x+1}=\dfrac{-5}{x-3}\)
b: |x|=1
=>x=-1(loại) hoặc x=1(nhận)
Khi x=1 thì \(A=\dfrac{-5}{1-3}=-\dfrac{5}{-2}=\dfrac{5}{2}\)
c: A=1/2
=>x-3=-10
=>x=-7
d: A nguyên
=>-5 chia hết cho x-3
=>x-3 thuộc {1;-1;5;-5}
=>x thuộc {4;2;8;-2}
a:
Sửa đề: \(P=\left(\dfrac{3+x}{3-x}-\dfrac{3-x}{3+x}-\dfrac{4x^2}{x^2-9}\right):\left(\dfrac{5}{3-x}-\dfrac{4x+2}{3x-x^2}\right)\)\(P=\left(\dfrac{-\left(x+3\right)}{x-3}+\dfrac{x-3}{x+3}-\dfrac{4x^2}{\left(x-3\right)\left(x+3\right)}\right):\dfrac{5x-4x-2}{x\left(3-x\right)}\)
\(=\dfrac{-x^2-6x-9+x^2-6x+9-4x^2}{\left(x-3\right)\left(x+3\right)}:\dfrac{x-2}{x\left(3-x\right)}\)
\(=\dfrac{-4x^2-12x}{\left(x-3\right)\left(x+3\right)}\cdot\dfrac{x\left(3-x\right)}{x-2}\)
\(=\dfrac{-4x\left(x+3\right)}{\left(x-3\right)\left(x+3\right)}\cdot\dfrac{-x\left(x-3\right)}{x-2}=\dfrac{4x^2}{x-2}\)
b: x^2-4x+3=0
=>x=1(nhận) hoặc x=3(loại)
Khi x=1 thì \(P=\dfrac{4\cdot1^2}{1-2}=-4\)
c: P>0
=>x-2>0
=>x>2
d: P nguyên
=>4x^2 chia hết cho x-2
=>4x^2-16+16 chia hết cho x-2
=>x-2 thuộc {1;-1;2;-2;4;-4;8;-8;16;-16}
=>x thuộc {1;4;6;-2;10;-6;18;-14}
a) \(A=\left(\frac{x+3}{x-9}+\frac{1}{\sqrt{x}+3}\right):\frac{\sqrt{x}}{\sqrt{x}-3}\)
\(=\left[\frac{x+3+\sqrt{x}-3}{\left(\sqrt{x}+3\right)\left(\sqrt{x}-3\right)}\right]:\frac{\sqrt{x}}{\sqrt{x}-3}\)
\(=\frac{\sqrt{x}\left(\sqrt{x}+1\right)}{\left(\sqrt{x}+3\right)\left(\sqrt{x}-3\right)}.\frac{\sqrt{x}-3}{\sqrt{x}}\)
\(=\frac{\sqrt{x}+1}{\sqrt{x}+3}\)
c) để A>1/3
\(\Rightarrow\frac{\sqrt{x}+3-2}{\sqrt{x}+3}>\frac{1}{3}\)
\(\Rightarrow\frac{2}{\sqrt{x}+3}>\frac{2}{3}\)
\(\Rightarrow\sqrt{x}+3>3\)
\(\Rightarrow x>0\)
a. Ta có \(A=\frac{3\sqrt{x}}{\sqrt{x}-3}=\frac{3\left(\sqrt{x}-3\right)}{\sqrt{x}-3}+\frac{9}{\sqrt{x}-3}\)
\(=3+\frac{9}{\sqrt{x}-3}\)
\(A\in Z\Rightarrow\sqrt{x}-3\inƯ\left(9\right)\Rightarrow\sqrt{x}-3\in\left\{-9;-3;-1;1;3;9\right\}\)
\(\Rightarrow\sqrt{x}\in\left\{0;2;4;6;12\right\}\Rightarrow x\in\left\{0;4;16;36;144\right\}\)
Vậy \(x\in\left\{0;4;16;36;144\right\}\)thì \(A\in Z\)
b. Thay \(x=7-4\sqrt{3}\Rightarrow A=\frac{3\sqrt{7-4\sqrt{3}}}{\sqrt{7-4\sqrt{3}}-3}\)
\(=\frac{3\sqrt{\left(2-\sqrt{3}\right)^2}}{\sqrt{\left(2-\sqrt{3}\right)^2}-3}=\frac{3\left(2-\sqrt{3}\right)}{2-\sqrt{3}-3}=\frac{15-9\sqrt{3}}{2}\)