2/3 -[-7/4-(1/2+3/8)]
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a) \(=\dfrac{254x\left(400-1\right)-145}{254+\left(400-1\right)x253}=\dfrac{254x400-254-145}{254+253x400-253}\)
\(=\dfrac{101600-399}{101200+1}=\dfrac{101211}{101201}=\dfrac{101201+10}{101201}=1+\dfrac{10}{101201}\)
b) \(=\dfrac{5392+\left(600+1\right)x5391}{5392x\left(600+1\right)-69}=\dfrac{5392+600x5391+5391}{5392x600+5392-69}\)
\(=\dfrac{10783+3234600}{3235200+5323}=\dfrac{\text{3245383}}{\text{3240523}}=\dfrac{3240523+60}{3240523}=1+\dfrac{60}{3240523}\)
c) \(=\dfrac{1}{2}x\left(\dfrac{1}{2}-\dfrac{1}{4}\right)+\dfrac{1}{2}x\left(\dfrac{1}{4}-\dfrac{1}{8}\right)+\dfrac{1}{32}\)
\(=\dfrac{1}{2}x\left(\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{8}\right)+\dfrac{1}{32}\)
\(=\dfrac{1}{2}x\left(\dfrac{1}{2}-\dfrac{1}{8}\right)+\dfrac{1}{32}=\dfrac{3}{16}+\dfrac{1}{32}=\dfrac{7}{32}\)
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Gọi a là chiều dài mảnh vườn (m)
Gọi b là chiều rộng mảnh vườn (m)
Theo đề bài ta có : \(a=\dfrac{3}{2}xb\)
Diện tích mảnh vườn HCN :
\(axb=\dfrac{3}{2}xbxb=54\Rightarrow bxb=54:\dfrac{3}{2}=54x\dfrac{2}{3}=36\)
\(\Rightarrow b=6\left(m\right)\Rightarrow a=\dfrac{3}{2}x6=9\left(m\right)\)
Chu vi mảnh vườn :
\(\left(9+6\right)x2=30\left(m\right)\)
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a) Thời gian người đi xe máy đuổi kịp người đi xe đạp :
\(15x2:\left(35-15\right)=1,5\left(h\right)\)
b) Chỗ gặp nhau cách A :
\(35x1,5=52,5\left(m\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(A=x^2+x+1\)
\(A=x^2+x+\dfrac{1}{4}-\dfrac{1}{4}+1\)
\(A=\left(x+\dfrac{1}{2}\right)^2+\dfrac{3}{4}\)
mà \(\left(x+\dfrac{1}{2}\right)^2\ge0\)
\(\Rightarrow A=\left(x+\dfrac{1}{2}\right)^2+\dfrac{3}{4}>\dfrac{3}{4}>0\) với mọi x
\(\Rightarrow Dpcm\)
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\(x:12=x:27\Rightarrow\dfrac{x}{12}=\dfrac{x}{27}\Rightarrow x\in\varnothing\)
\(\dfrac{2}{3}-\left[\dfrac{7}{4}-\left(\dfrac{1}{2}+\dfrac{3}{8}\right)\right]\)
\(=\dfrac{2}{3}-\left[\dfrac{7}{4}-\left(\dfrac{4}{8}+\dfrac{3}{8}\right)\right]\)
\(=\dfrac{2}{3}-\left(\dfrac{7}{4}-\dfrac{7}{8}\right)=\dfrac{2}{3}-\left(\dfrac{14}{8}-\dfrac{7}{8}\right)=\dfrac{2}{3}-\dfrac{14}{8}=\dfrac{16}{24}-\dfrac{42}{24}=\dfrac{-26}{24}=-\dfrac{13}{12}\)