Cho x≠0,2,-2,Rút gọn rồi tính GTBT
A= (\(\dfrac{4}{x-2}\)-\(\dfrac{3}{x+2}\)) :\(\dfrac{x+14}{x^2}\). (Tại x= -3 )
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28 tháng 7 2021
a) Ta có: \(\dfrac{3x^2-12x+12}{x^2-4}\)
\(=\dfrac{3\left(x^2-4x+4\right)}{\left(x-2\right)\left(x+2\right)}\)
\(=\dfrac{3\left(x-2\right)^2}{\left(x-2\right)\left(x+2\right)}\)
\(=\dfrac{3\left(x-2\right)}{x+2}\)
\(=\dfrac{3\cdot\left(\dfrac{-1}{4}-2\right)}{\dfrac{-1}{4}+2}=-\dfrac{27}{7}\)
b) Ta có: \(\dfrac{x^2-5x-6}{x^2-9}\)
\(=\dfrac{\left(x-6\right)\left(x+1\right)}{\left(x-3\right)\left(x+3\right)}\)
\(=\dfrac{\left(-1-6\right)\left(-1+1\right)}{\left(-1-3\right)\left(-1+3\right)}\)
=0
28 tháng 7 2021
a) \(\dfrac{9x^2-6x+1}{9x^2-1}\)
\(=\dfrac{\left(3x-1\right)^2}{\left(3x-1\right)\left(3x+1\right)}\)
\(=\dfrac{3x-1}{3x+1}\)
\(=\dfrac{3\cdot\left(-3\right)-1}{3\cdot\left(-3\right)+1}=\dfrac{-9-1}{-9+1}=\dfrac{-10}{-8}=\dfrac{5}{4}\)
b) Ta có: \(\dfrac{x^2-6x+9}{3x^2-9x}\)
\(=\dfrac{\left(x-3\right)^2}{3x\left(x-3\right)}\)
\(=\dfrac{x-3}{3x}\)
\(=\dfrac{-\dfrac{1}{3}-3}{3\cdot\dfrac{-1}{3}}=\dfrac{-\dfrac{10}{3}}{-1}=\dfrac{10}{3}\)
c) Ta có: \(\dfrac{x^2-4x+4}{2x^2-4x}\)
\(=\dfrac{\left(x-2\right)^2}{2x\left(x-2\right)}\)
\(=\dfrac{x-2}{2x}\)
\(=\dfrac{\dfrac{-1}{2}-2}{2\cdot\dfrac{-1}{2}}=\dfrac{-\dfrac{5}{2}}{-1}=\dfrac{5}{2}\)
13 tháng 8 2021
Ta có: \(\sqrt{\dfrac{\left(x-3\right)^2}{\left(3-x\right)^2}}+\dfrac{x^2-1}{x-3}\)
\(=\dfrac{\left|x-3\right|}{\left|3-x\right|}+\dfrac{x^2-1}{x-3}\)
\(=\dfrac{3-x}{x-3}+\dfrac{x^2-1}{x-3}\)
\(=\dfrac{x^2-x+2}{x-3}\)
\(=\dfrac{-7}{10}\)
HH
1
29 tháng 7 2021
\(\dfrac{x^2-9y^2}{x^2-6xy+9y^2}\) tại x = 1 , y = -\(\dfrac{2}{3}\)
= \(\dfrac{x^2-\left(3y\right)^2}{\left(x-3y\right)^2}\)
= \(\dfrac{\left(x-3y\right)\left(x+3y\right)}{\left(x-3y\right)}\)
= (x + 3y)
Thay x = 1 , y = -\(\dfrac{2}{3}\) vào
x + 3y
= 1 +3 . -\(\dfrac{2}{3}\)
= -1
Chúc bạn học tốt
AT
10 tháng 7 2021
a) \(P=\dfrac{x^2+3x}{x^2-8x+16}:\left(\dfrac{x+4}{x}+\dfrac{1}{x-4}+\dfrac{19-x^2}{x^2-4x}\right)\left(x\ne0,x\ne4\right)\)
\(=\dfrac{x^2+3x}{\left(x-4\right)^2}:\left(\dfrac{x+4}{x}+\dfrac{1}{x-4}+\dfrac{19-x^2}{x\left(x-4\right)}\right)\)
\(=\dfrac{x^2+3x}{\left(x-4\right)^2}:\dfrac{\left(x+4\right)\left(x-4\right)+x+19-x^2}{x\left(x-4\right)}\)
\(=\dfrac{x^2+3x}{\left(x-4\right)^2}:\dfrac{x+3}{x\left(x-4\right)}=\dfrac{x\left(x+3\right)}{\left(x-4\right)^2}.\dfrac{x\left(x-4\right)}{x+3}=\dfrac{x^2}{x-4}\)
b) \(x=\sqrt{4+2\sqrt{3}}-\sqrt{4-2\sqrt{3}}=\sqrt{\left(\sqrt{3}+1\right)^2}-\sqrt{\left(\sqrt{3}-1\right)^2}\)
\(=\sqrt{3}+1-\sqrt{3}+1=2\)
\(\Rightarrow P=\dfrac{2^2}{2-4}=-2\)
10 tháng 7 2021
a)\(ĐKXĐ:\left\{{}\begin{matrix}x\left(x-4\right)\ne0\\\dfrac{x+4}{x}+\dfrac{1}{x-4}+\dfrac{19-x^2}{x^2-4x}\ne0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x\ne4\\x\ne0\\x\ne-3\end{matrix}\right.\)
\(P=\dfrac{x\left(x+3\right)}{\left(x-4\right)}:\left(\dfrac{x^2-16+x+19-x^2}{x\left(x-4\right)}\right)=\dfrac{x\left(x+3\right)}{\left(x-4\right)^2}.\left(\dfrac{x\left(x-4\right)}{x+3}\right)=\dfrac{x^2}{x-4}\)
b)\(x=\sqrt{4+2\sqrt{3}}-\sqrt{4-2\sqrt{3}}=\sqrt{\left(\sqrt{3}+1\right)^2}=\sqrt{3+1}-\left(\sqrt{3}-1\right)=2\)
thay x=2 vào P ta có \(P=\dfrac{2^2}{2-4}=-2\)
26 tháng 7 2023
a: ĐKXĐ: x>0; x<>4
\(P=\left(2-\sqrt{x}+2\right)\cdot\dfrac{1}{\sqrt{x}-2}=\dfrac{4-\sqrt{x}}{\sqrt{x}-2}\)
b: P=2/3
=>(4-căn x)/(căn x-2)=2/3
=>2căn x-4=12-3căn x
=>5căn x=16
=>x=256/25
c: Khi x=8-2căn 7 thì \(P=\dfrac{4-\sqrt{7}+1}{\sqrt{7}-1-2}=\dfrac{5-\sqrt{7}}{\sqrt{7}-3}=-4-\sqrt{7}\)
\(A=\left(\dfrac{4}{x-2}-\dfrac{3}{x+2}\right):\dfrac{x+14}{x^2}\\ =\left(\dfrac{4\left(x+2\right)}{\left(x-2\right)\left(x+2\right)}-\dfrac{3\left(x-2\right)}{\left(x+2\right)\left(x-2\right)}\right)\cdot\dfrac{x^2}{x+14}\\ =\dfrac{4x+8-3x+6}{\left(x-2\right)\left(x+2\right)}\cdot\dfrac{x^2}{x+14}\\ =\dfrac{x+14}{\left(x-2\right)\left(x+2\right)}\cdot\dfrac{x^2}{x+14}\\=\dfrac{x^2}{x^2-4}\)
Tại `x=-3` Ta có :
\(\dfrac{x^2}{x^2-4}\\ =\dfrac{-3^2}{-3^2-4}\\ =\dfrac{9}{9-4}\\ =\dfrac{9}{5}\)