cho biểu thức B=\(\dfrac{6\sqrt{y}+9}{y\sqrt{y}-27}-\dfrac{\sqrt{y}-2}{y+\sqrt{y}-6}+\dfrac{1}{\sqrt{y}+\dfrac{9}{\sqrt{y}}+3}\)
a.Rút gọn biểu thức B
b.Tìm giá trị nguyên của y để B<-1
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2 tháng 10 2021
a: ĐKXĐ: \(\left\{{}\begin{matrix}y\ge0\\y\ne1\end{matrix}\right.\)
Ta có: \(P=\left(\dfrac{1}{1-\sqrt{y}}+\dfrac{1}{1+\sqrt{y}}\right):\left(\dfrac{1}{1-\sqrt{y}}-\dfrac{1}{1+\sqrt{y}}\right)+\dfrac{1}{1-\sqrt{y}}\)
\(=\dfrac{1+\sqrt{y}+1-\sqrt{y}}{\left(1-\sqrt{y}\right)\left(1+\sqrt{y}\right)}:\dfrac{1+\sqrt{y}-1+\sqrt{y}}{\left(1-\sqrt{y}\right)\left(1+\sqrt{y}\right)}+\dfrac{1}{1-\sqrt{y}}\)
\(=\dfrac{2}{2\sqrt{y}}-\dfrac{1}{\sqrt{y}-1}\)
\(=\dfrac{\sqrt{y}-1-\sqrt{y}}{\sqrt{y}\left(\sqrt{y}-1\right)}\)
\(=\dfrac{-1}{\sqrt{y}\left(\sqrt{y}-1\right)}\)
Q
23 tháng 4 2021
2)
\(A=\dfrac{5\sqrt{a}-3}{\sqrt{a}-2}+\dfrac{3\sqrt{a}+1}{\sqrt{a}+2}-\dfrac{a^2+2\sqrt{a}+8}{a-4}\)
\(=\dfrac{\left(5\sqrt{a}-3\right)\left(\sqrt{a}+2\right)+\left(3\sqrt{a}+1\right)\left(\sqrt{a}-2\right)-a^2-2\sqrt{a}-8}{\left(\sqrt{a}-2\right)\left(\sqrt{a}+2\right)}\)
\(=\dfrac{5a+10\sqrt{a}-3\sqrt{a}-6+3a-6\sqrt{a}+\sqrt{a}-2-a^2-2\sqrt{a}-8}{\left(\sqrt{a}-2\right)\left(\sqrt{a}+2\right)}\)
\(=\dfrac{-a^2+8a-16}{\left(\sqrt{a}-2\right)\left(\sqrt{a}+2\right)}=\dfrac{-\left(a-4\right)^2}{a-4}=4-a\)
23 tháng 4 2021
1: Ta có: \(\left\{{}\begin{matrix}3x-y=2m-1\\x+y=3m+2\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}4x=5m+1\\x+y=3m+2\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{5m+1}{4}\\y=3m+2-x\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{5m+1}{4}\\y=\dfrac{12m+8-5m-1}{4}=\dfrac{7m+7}{4}\end{matrix}\right.\)
Ta có: \(x^2+2y^2=9\)
\(\Leftrightarrow\left(\dfrac{5m+1}{4}\right)^2+2\cdot\left(\dfrac{7m+7}{4}\right)^2=9\)
\(\Leftrightarrow\dfrac{25m^2+10m+1}{16}+\dfrac{2\cdot\left(49m^2+98m+49\right)}{16}=9\)
\(\Leftrightarrow25m^2+10m+1+98m^2+196m+98-144=0\)
\(\Leftrightarrow123m^2+206m-45=0\)
Đến đây bạn tự làm nhé, chỉ cần giải phương trình bậc hai bằng delta thôi
19 tháng 12 2018
a) Để B có nghĩa thì \(\left\{{}\begin{matrix}y\ge0\\y\ne1\end{matrix}\right.\)
B=\(\left(\dfrac{1}{\sqrt{y}+1}-\dfrac{3\sqrt{y}}{\sqrt{y}-1}+3\right).\dfrac{\sqrt{y}+1}{\sqrt{y}+2}=\left[\dfrac{\sqrt{y}-1}{\left(\sqrt{y}+1\right)\left(\sqrt{y}-1\right)}-\dfrac{3\sqrt{y}\left(\sqrt{y}+1\right)}{\left(\sqrt{y}+1\right)\left(\sqrt{y}-1\right)}+\dfrac{3\left(\sqrt{y}+1\right)\left(\sqrt{y}-1\right)}{\left(\sqrt{y}+1\right)\left(\sqrt{y}-1\right)}\right].\dfrac{\sqrt{y}+1}{\sqrt{y}+2}=\left[\dfrac{\sqrt{y}-1}{\left(\sqrt{y}+1\right)\left(\sqrt{y}-1\right)}-\dfrac{3y+3\sqrt{y}}{\left(\sqrt{y}+1\right)\left(\sqrt{y}-1\right)}+\dfrac{3y-3}{\left(\sqrt{y}+1\right)\left(\sqrt{y}-1\right)}\right].\dfrac{\sqrt{y}+1}{\sqrt{y}+2}=\dfrac{\sqrt{y}-1-3y-3\sqrt{y}+3y-3}{\left(\sqrt{y}+1\right)\left(\sqrt{y}-1\right)}.\dfrac{\sqrt{y}+1}{\sqrt{y}+2}=\dfrac{\left(-2\sqrt{y}-4\right)\left(\sqrt{y}+1\right)}{\left(\sqrt{y}+1\right)\left(\sqrt{y}-1\right)\left(\sqrt{y}+2\right)}=\dfrac{-2\left(\sqrt{y}+2\right)\left(\sqrt{y}+1\right)}{\left(\sqrt{y}+1\right)\left(\sqrt{y}-1\right)\left(\sqrt{y}+2\right)}=\dfrac{-2}{\sqrt{y}-1}=\dfrac{2}{1-\sqrt{y}}\)
b) Ta có y=\(3+2\sqrt{2}\Rightarrow P=\dfrac{2}{1-\sqrt{3+2\sqrt{2}}}=\dfrac{2}{1-\sqrt{2+2\sqrt{2}+1}}=\dfrac{2}{1-\sqrt{\left(\sqrt{2}+1\right)^2}}=\dfrac{2}{1-\sqrt{2}-1}=\dfrac{2}{-\sqrt{2}}=-\sqrt{2}\)
Vậy khi x=\(3+2\sqrt{2}\) thì \(P=-\sqrt{2}\)
LT
22 tháng 6 2021
\(A=\left(\dfrac{4\sqrt{y}}{2+\sqrt{y}}+\dfrac{8y}{4-y}\right):\left(\dfrac{\sqrt{y}-1}{y-2\sqrt{y}}-\dfrac{2}{\sqrt{y}}\right)\)
\(A=\dfrac{4\sqrt{y}\left(2-\sqrt{y}\right)+8y}{\left(2+\sqrt{y}\right)\left(2-\sqrt{y}\right)}:\dfrac{\sqrt{y}-1-2\left(\sqrt{y}-2\right)}{\sqrt{y}\left(\sqrt{y}-2\right)}\)
\(A=\dfrac{8\sqrt{y}+4y}{\left(2+\sqrt{y}\right)\left(2-\sqrt{y}\right)}.\dfrac{\sqrt{y}\left(\sqrt{y}-2\right)}{-\sqrt{y}+3}\)
\(A=\dfrac{4\sqrt{y}}{2-\sqrt{y}}.\dfrac{\sqrt{y}\left(2-\sqrt{y}\right)}{\sqrt{y}-3}\)
\(A=\dfrac{4y}{\sqrt{y}-3}\)
Chúc bạn học tốt ^^
12 tháng 11 2021
5: \(=\dfrac{1}{x-y}\cdot x^3\cdot\left(x-y\right)^2=x^3\left(x-y\right)\)