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a) đề kiểu gì vậy bạn
b) \(x+\frac{2}{14}=\frac{3}{21}\Leftrightarrow x=0\)
c) \(x+\frac{2}{7}=\frac{1}{2}\Leftrightarrow x=\frac{3}{14}\)
d) \(\frac{12}{15}=\frac{x-5}{10}\Leftrightarrow15x-75=120\Leftrightarrow15x=195\Leftrightarrow x=13\)
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` 1, 5 . ( -2/25 = 3/2 . (-2)/25 = -6/50 = -3/25 `
` 1 3/5 . (-3)/4 = 8/5 . (-3)/4 = -24/20 = -6/5 `
`-15/4 : 21/(-1) = -15/4 . (-1)/21 = 15/84 = 5/28 `
` ( -2 1/7 ) : ( -1 1/14 ) = (-15)/7 : (-15)/14 = -15/7 . (-14)/15 = 210/105 = 2 `
`@animephamdanhv.`
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\(\frac{-2}{7}\div\frac{15}{14}=\frac{-21}{20}\div\left(5\times x\right)\)
\(\Rightarrow\frac{-4}{15}=\frac{-21}{20}\div\left(5\times x\right)\)
\(\Rightarrow5\times x=\frac{-21}{20}\div\frac{-4}{15}\)
\(\Rightarrow5\times x=\frac{63}{16}\)
\(\Rightarrow x=\frac{63}{16}\div5\)
\(\Rightarrow x=\frac{63}{80}\)
~ học tốt nha ~
\(\frac{-2}{7}:\frac{15}{14}=\frac{-21}{20}:(5\cdot x)\)
\(\Leftrightarrow\frac{-21}{20}:(5\cdot x)=\frac{-2}{7}:\frac{15}{14}\)
\(\Leftrightarrow\frac{-21}{20}:(5\cdot x)=\frac{-2}{7}\cdot\frac{14}{15}\)
\(\Leftrightarrow\frac{-21}{20}:(5\cdot x)=\frac{-2}{1}\cdot\frac{2}{15}\)
\(\Leftrightarrow\frac{-21}{20}:(5\cdot x)=\frac{4}{15}\)
\(\Leftrightarrow5\cdot x=\frac{-21}{20}:\frac{4}{15}\)
\(\Leftrightarrow5\cdot x=\frac{-21}{20}\cdot\frac{15}{4}\)
\(\Leftrightarrow5\cdot x=\frac{-21}{4}\cdot\frac{3}{4}\)
\(\Leftrightarrow5\cdot x=\frac{-63}{16}\)
\(\Leftrightarrow x=\frac{-63}{16}:5\)
\(\Leftrightarrow x=\frac{-63}{16}\cdot\frac{1}{5}=\frac{-63}{80}\)
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\(\dfrac{x-2023}{6}+\dfrac{x-2023}{10}+\dfrac{x-2023}{15}+\dfrac{x-2023}{21}=\dfrac{8}{21}\)
\(\left(x-2023\right)\left(\dfrac{1}{6}+\dfrac{1}{10}+\dfrac{1}{15}+\dfrac{1}{21}\right)=\dfrac{8}{21}\)
\(\left(x-2023\right).\dfrac{8}{21}=\dfrac{8}{21}\)
\(x-2023=1\)
\(x=2024\)
Vậy..............
\(...\Rightarrow\left(x-2023\right)\left(\dfrac{1}{6}+\dfrac{1}{10}+\dfrac{1}{15}+\dfrac{1}{21}\right)=\dfrac{8}{21}\)
\(\Rightarrow\left(x-2023\right)\left(\dfrac{35+21+14+1}{210}\right)=\dfrac{8}{21}\)
\(\Rightarrow\left(x-2023\right).\dfrac{71}{210}=\dfrac{8}{21}\)
\(\Rightarrow\left(x-2023\right).\dfrac{71}{210}=\dfrac{8}{21}.\dfrac{210}{71}=\dfrac{80}{71}\)
\(\Rightarrow x-2023=\dfrac{80}{71}\Rightarrow x=\dfrac{80}{71}+2023=\dfrac{143713}{71}\)
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- a, Do |x|=14
=> \(\orbr{\begin{cases}x=14\\x=-14\end{cases}}\)
- b, Do |x-3| =11
=> \(\orbr{\begin{cases}x-3=11\\x-3=-11\end{cases}}\)
=> \(\orbr{\begin{cases}x=14\\x=-8\end{cases}}\)
- c, Do |5-2x|=15
=> \(\orbr{\begin{cases}5-2x=15\\5-2x=-15\end{cases}}\)
=> \(\orbr{\begin{cases}2x=-10\\2x=20\end{cases}}\)
=> \(\orbr{\begin{cases}x=-5\\x=10\end{cases}}\)
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Lời giải:
Đặt \(\frac{10}{x-5}=\frac{6}{y-9}=\frac{14}{z-21}=\frac{1}{k}\) với $k\neq 0$
$\Rightarrow x=10k+5; y=6k+9; z=14k+21$
Khi đó:
$xyz=6720$
$\Leftrightarrow (10k+5)(6k+9)(14k+21)=6720$
$\Leftrightarrow (2k+1)(2k+3)(2k+3)=64$
Đây là PT bậc 3 và nghiệm rất xấu. PP giải cũng phù hợp với lớp 9 chứ không phù hợp với lớp 7.
Do đó ta tìm giá trị gần đúng của $k$. $k\approx 0,89$
$\Rightarrow x\approx 13,95; y\approx 14,37; z\approx 33,53$
\(-\frac{15}{14}:x=x:-\frac{10}{21}\)
#) Giải ( Ko biết có đúng ko )
\(x:x=-\frac{15}{14}:-\frac{10}{21}\)
\(x:x=\frac{9}{4}\)
~ Hok tốt ~