tìm x,y: x\6 - 1\y =1\2 (lưu ý :dấu \ này là chỉ phân số)
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\(\left(x-1\right)^2+\left|2y-x\right|=0\)
có \(\hept{\begin{cases}\left(x-1\right)^2\ge0\\\left|2y-x\right|\ge0\end{cases}}\)
\(\Rightarrow\hept{\begin{cases}x-1=0\\2y-x=0\end{cases}\Leftrightarrow\hept{\begin{cases}x=1\\2y-1=0\end{cases}}\Leftrightarrow\hept{\begin{cases}x=1\\y=\frac{1}{2}\end{cases}}}\)
vậy_
\(b,\left(2x+1\right).\left(39-2\right)=-55\)
\(\Rightarrow\left(2x+1\right).37=-55\)
\(\Rightarrow3x+1=-\frac{55}{37}\)
\(\Rightarrow3x=-\frac{92}{37}\)
\(\Rightarrow x=-\frac{92}{111}\)
\(c,\left(x-7\right)\left(x+3\right)< 0\)
\(\Rightarrow\orbr{\begin{cases}x-7>0;x+3< 0\\x-7< 0;x+3>0\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}x>7;x< -3\\x< 7;x>-3\end{cases}}\)
Giải:
a) \(\dfrac{-5}{8}=\dfrac{x}{16}\)
\(\Rightarrow x=\dfrac{16.-5}{8}=-10\)
\(\dfrac{3x}{9}=\dfrac{2}{6}\)
\(\Rightarrow3x=\dfrac{2.9}{6}=3\)
\(\Rightarrow x=1\)
b) \(\dfrac{x+3}{15}=\dfrac{1}{3}\)
\(\Rightarrow x+3=\dfrac{1.15}{3}=5\)
\(\Rightarrow x=2\)
\(\dfrac{6}{2x+1}=\dfrac{2}{7}\)
\(\Rightarrow2x+1=\dfrac{6.7}{2}=21\)
\(\Rightarrow x=10\)
c) \(\dfrac{4}{x-6}=\dfrac{y}{24}=\dfrac{-12}{18}\)
\(\Rightarrow\dfrac{4}{x-6}=\dfrac{-12}{18}\)
\(\Rightarrow x-6=\dfrac{18.4}{-12}=-6\)
\(\Rightarrow x=0\)
\(\Rightarrow\dfrac{y}{24}=\dfrac{-12}{18}\)
\(\Rightarrow y=\dfrac{-12.24}{18}=-16\)
\(\dfrac{3-x}{-12}=\dfrac{16}{y+1}=\dfrac{192}{-72}\)
\(\Rightarrow\dfrac{3-x}{-12}=\dfrac{192}{-72}\)
\(\Rightarrow3-x=\dfrac{192.-12}{-72}=32\)
\(\Rightarrow x=-29\)
\(\Rightarrow\dfrac{16}{y+1}=\dfrac{192}{-72}\)
\(\Rightarrow y+1=\dfrac{16.-72}{192}=-6\)
d) \(\dfrac{-2}{3}< \dfrac{x}{5}< \dfrac{-1}{6}\)
\(\Rightarrow\dfrac{-20}{30}< \dfrac{6x}{30}< \dfrac{-5}{30}\)
\(\Rightarrow6x\in\left\{-18;-12;-6\right\}\)
\(\Rightarrow x\in\left\{-3;-2;-1\right\}\)
\(\dfrac{-1}{5}\le\dfrac{x}{8}\le\dfrac{1}{4}\)
\(\Rightarrow\dfrac{-8}{40}\le\dfrac{5x}{40}\le\dfrac{10}{40}\)
\(\Rightarrow5x\in\left\{-5;0;5;10\right\}\)
\(\Rightarrow x\in\left\{-1;0;1;2\right\}\)
e) \(\dfrac{x+46}{20}=x\dfrac{2}{5}\)
\(\Rightarrow\dfrac{x+46}{20}=x+\dfrac{2}{5}\)
\(\Rightarrow\dfrac{x+46}{20}=\dfrac{5x+2}{5}\)
\(\Rightarrow5.\left(x+46\right)=20.\left(5x+2\right)\)
\(\Rightarrow5x+230=100x+40\)
\(\Rightarrow5x-100x=40-230\)
\(\Rightarrow-95x=-190\)
\(\Rightarrow x=-190:-95\)
\(\Rightarrow x=2\)
\(y\dfrac{5}{y}=\dfrac{86}{y}\)
\(\Rightarrow y+\dfrac{5}{y}=\dfrac{86}{y}\)
\(\Rightarrow\dfrac{y^2+5}{y}=\dfrac{86}{y}\)
\(\Rightarrow y^2+5=86\)
\(\Rightarrow y^2=86-5\)
\(\Rightarrow y^2=81\)
\(\Rightarrow\left[{}\begin{matrix}y=9\\y=-9\end{matrix}\right.\)
Chúc bạn học tốt!
\(A=\left|x+12\right|+\left(y+2\right)^2+11\ge11\)
ta có \(\hept{\begin{cases}\left|x+12\right|\ge0\\\left(y+2\right)^2\ge0\end{cases}}\)
\(\Rightarrow\left|x+12\right|+\left(y+2\right)^2+11\ge11\)
\(\Rightarrow A_{min}=11\Leftrightarrow\hept{\begin{cases}x+12=0\\y+2=0\end{cases}\Rightarrow\hept{\begin{cases}x=-12\\y=-2\end{cases}}}\)
\(\frac{x}{5}-\frac{3}{7}=\frac{10}{13}\)
\(\Rightarrow\frac{91x}{455}-\frac{195}{455}=\frac{350}{455}\)
\(\Rightarrow91x-195=350\)
\(\Rightarrow91x=545\)
\(\Rightarrow x=\frac{545}{91}\)
\(\frac{-3x}{4}+\frac{1}{3}=\frac{11}{5}\)
\(\Rightarrow\frac{-45x}{60}+\frac{20}{60}=\frac{132}{60}\)
\(\Rightarrow-45x+20=132\)
\(\Rightarrow-45x=112\)
\(\Rightarrow x=-\frac{112}{45}\)
b: \(=\dfrac{\left(x+3\right)^2-y^2}{2\left(x-y+3\right)}\)
\(=\dfrac{\left(x+3+y\right)\left(x+3-y\right)}{2\left(x-y+3\right)}=\dfrac{x+y+3}{2}\)
\(\frac{x}{6}-\frac{1}{y}=\frac{xy-6}{6y}=\frac{1}{2}\)
\(\Leftrightarrow xy-6=3y\)
\(\Leftrightarrow y\left(x-3\right)=6=1.6=2.3\)
Bảng giá trị: