Bài 2:
a) \(\dfrac{1}{3}+\dfrac{2}{3}x=0,5\Rightarrow\dfrac{2}{3}x=0,5-\dfrac{1}{3}=\dfrac{1}{6}\Rightarrow x=\dfrac{1}{6}:\dfrac{2}{3}=\dfrac{1}{4}\)
b) \(\dfrac{3x-2}{2}=\dfrac{8}{3x-2}\left(đk:x\ne\dfrac{2}{3}\right)\)
\(\Rightarrow\left(3x-2\right)^2=2.8=16\)
\(\Rightarrow\left[{}\begin{matrix}3x-2=4\\3x-2=-4\end{matrix}\right.\)\(\Rightarrow\left[{}\begin{matrix}x=2\left(tm\right)\\x=-\dfrac{2}{3}\left(tm\right)\end{matrix}\right.\)
c) \(1-\left|\sqrt{\dfrac{1}{16}}-x\right|=-3^2\)
\(\Rightarrow\left|\dfrac{1}{4}-x\right|=1+3^2=1+9=10\)
\(\Rightarrow\left[{}\begin{matrix}\dfrac{1}{4}-x=10\\\dfrac{1}{4}-x=-10\end{matrix}\right.\)\(\Rightarrow\left[{}\begin{matrix}x=-\dfrac{39}{4}\\x=\dfrac{41}{4}\end{matrix}\right.\)
Bài 3:
Gọi số HS 3 lớp 7A,7B,7C lần lượt là a,b,c(học sinh)(a,b,c∈N*)
Áp dụng t/c dtsbn:
\(\dfrac{a}{11}=\dfrac{b}{12}=\dfrac{c}{13}=\dfrac{c-a}{13-11}=\dfrac{6}{2}=3\)
\(\Rightarrow\left\{{}\begin{matrix}a=11.3=33\\b=12.3=36\\b=13.3=39\end{matrix}\right.\)
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