Tìm x, biết:x+5 phần 48 = 7 phần 42
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\(x\left(x+5\right)\left(x-5\right)-\left(x+2\right)\left(x^2-2x+4\right)=42\)
\(\Leftrightarrow x\left(x^2-25\right)-\left(x^3+8\right)=42\)
\(\Leftrightarrow x^3-25x-x^3-8=42\)
\(\Leftrightarrow-25x-8=42\)
\(\Leftrightarrow-25x=42+8\)
\(\Leftrightarrow-25x=50\)
\(\Leftrightarrow x=-\dfrac{50}{25}=-2\)
\(\dfrac{x}{5}=\dfrac{y}{7}=\dfrac{z}{2}=\dfrac{y-x}{7-5}=\dfrac{48}{2}=24\\ \Rightarrow\left\{{}\begin{matrix}x=120\\y=168\\z=48\end{matrix}\right.\)
\(\dfrac{x}{5}=\dfrac{y}{7}=\dfrac{z}{2}=\dfrac{y-x}{7-5}=\dfrac{48}{2}=24\)
\(\Rightarrow x=5.24=\)120
\(y=7.24=\)168
\(z=2.24=48\)
\(x+\frac{x}{3}=24\)
\(\frac{3x+x}{3}=\frac{72}{3}\)
\(4x=72\)
\(x=18\)
7/48 - (1/2 x 2 + 1/6 x 4 + 1/8 x 5 + 1/12 x 7 + 1/14 x 8) : x = 0
7/48 - (1 + 2/3 + 5/8 + 7/12 + 4/7) : x = 0 (đã rút gọn)
7/48 - (336/336 + 224/336 + 210/336 + 196/336 + 192/336) : x = 0 (quy đồng)
7/48 - 193/56 : x = 0
193/56 : x = 0 + 7/48
193/56 : x = 7/48
x = 193/56 : 7/48
x = 1158/49
\(\frac{12x-15y}{7}=\frac{20z-12x}{9}=\frac{15y-20z}{11}=\frac{12x-15y+20z-12x+15y-20z}{7+9+11}=0\)
\(12x-15y=0\Rightarrow4x=5y\Rightarrow\frac{x}{5}=\frac{y}{4}\)
\(20z-12x=0\Rightarrow5z=3x\Rightarrow\frac{z}{3}=\frac{x}{5}\)
\(15y-20z=0\Rightarrow3y=4z\Rightarrow\frac{y}{4}=\frac{z}{3}\)
\(\Rightarrow\frac{x}{5}=\frac{y}{4}=\frac{z}{3}=\frac{x+y+z}{5+4+3}=\frac{48}{12}=4\)
ta có;x=4x5=20
y=4x4=16
z=4x3=12
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ta có :
\(12\times x=42:\frac{1}{10}\)
ha y \(12\times x=42\times10=420\) nên : \(x=420:12=35\)
Vậy x = 35
\(\frac{x-3}{x+5}=\frac{5}{7}\Rightarrow7\cdot\left(x-3\right)=5\cdot\left(x+5\right)\Rightarrow7x-21=5x+25\Rightarrow7x-5x=25+21\Rightarrow2x=46\Rightarrow x=\frac{46}{2}=23\)
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