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1a) \(\frac{x-3}{x+7}=\frac{-5}{-6}\)
=> \(\frac{x-3}{x+7}=\frac{5}{6}\)
=> (x - 3).6 = 5.(x + 7)
=> 6x - 18 = 5x + 35
=> 6x - 5x = 35 + 18
=> x = 53
b) \(\frac{x-7}{x+3}=\frac{4}{3}\)
=> (x - 7). 3 = (x + 3). 4
=> 3x - 21 = 4x + 12
=> 3x - 4x = 12 + 21
=> -x = 33
=> x = -33
c) \(\frac{x-10}{6}=-\frac{5}{18}\)
=> (x - 10) . 18 = -5 . 6
=> 18x - 180 = -30
=> 18x = -30 + 180
=> 18x = 150
=> x = 150 : 18 = 25/3
d) \(\frac{x-2}{4}=\frac{25}{x-2}\)
=> (x - 2)(x - 2) = 25 . 4
=> (x - 2)2 = 100
=> (x - 2)2 = 102
=> \(\orbr{\begin{cases}x-2=10\\x-2=-10\end{cases}}\)
=> \(\orbr{\begin{cases}x=12\\x=-8\end{cases}}\)
e) \(\frac{7}{x}=\frac{x}{28}\)
=> 7 . 28 = x . x
=> 196 = x2
=> x2 = 142
=> \(\orbr{\begin{cases}x=14\\x=-14\end{cases}}\)
f) \(\frac{40+x}{77-x}=\frac{6}{7}\)
=> (40 + x) . 7 = (77 - x).6
=> 280 + 7x = 462 - 6x
=> 280 - 462 = -6x + 7x
=> -182 = x
=> x = -182
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l) (x + 9) . (x2 – 25) = 0
<=> (x + 9) . (x – 5) . (x + 5) = 0
<=> \(\left[{}\begin{matrix}\text{x + 9 = 0}\\x-5=0\\x+5=0\end{matrix}\right.\left[{}\begin{matrix}x=-9\\x=5\\x=-5\end{matrix}\right.\)
Vậy S = \(\left\{-9,5,-5\right\}\)
e) |x - 4 |< 7
<=> \(\left[{}\begin{matrix}x-4=7\\x-4=-7\end{matrix}\right.< =>\left[{}\begin{matrix}x=11\\x=-3\end{matrix}\right.\)
Vậy S = \(\left\{11;-3\right\}\)
I,(x+9).(x^2-25)=0
tương đương:x+9=0
x^2-25=0
tương đương : x=-9
x=5
e,\(\left|x-4\right|\)=7
tương đương x-4=4
x-4=-4
tương đương :x=0
x=-8
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a,\(\left(\frac{7}{5}-2x\right).\frac{40}{20}=\frac{8}{14}\)
\(\Rightarrow\left(\frac{7}{5}-2x\right).2=\frac{4}{7}\)
\(\Rightarrow\frac{7}{5}-2x=\frac{4}{7}:2\)
\(\Rightarrow\frac{7}{5}-2x=\frac{2}{7}\)
\(\Rightarrow2x=\frac{7}{5}-\frac{2}{7}\)
\(\Rightarrow2x=\frac{39}{35}\)
\(\Rightarrow x=\frac{39}{35}:2\)
\(\Rightarrow x=\frac{39}{70}\)
b, \(\frac{7}{2}.x-20\%.x=-4\)
\(\Rightarrow x\left(\frac{7}{2}-20\%\right)=-4\)
\(\Rightarrow x\left(\frac{7}{2}-\frac{1}{5}\right)=-4\)
\(\Rightarrow x\frac{7}{10}=-4\)
\(\Rightarrow x=-4:\frac{7}{10}\)
\(\Rightarrow x=-\frac{40}{7}\)
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3: Số học sinh giỏi là 40*1/5=8 bạn
Số học sinh trung bình là 32*3/8=12 bạn
Số học sinh khá là 32-12=20 bạn
1:
a: -1/3+7/6=7/6-2/6=5/6
b: 5/7-3/5=25/35-21/35=4/35
c: 0,75*4/5=4/5*3/4=3/5
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a) Áp dụng tính chất dãy tỉ số bằng nhau ta có:
\(\dfrac{x}{7}=\dfrac{y}{6}=\dfrac{x-y}{7-6}=\dfrac{80}{1}=80\)
\(\Rightarrow\dfrac{x}{7}=80\Rightarrow x=80\cdot7=560\)
\(\Rightarrow\dfrac{y}{6}=80\Rightarrow y=80\cdot6=480\)
b) Áp dụng tính chất dãy tỉ số bằng nhau ta có::
\(\dfrac{x}{4}=\dfrac{y}{7}=\dfrac{x+y}{4+7}=\dfrac{12}{11}\)
\(\Rightarrow\dfrac{x}{4}=\dfrac{12}{11}\Rightarrow x=\dfrac{4\cdot12}{11}=\dfrac{48}{11}\)
\(\Rightarrow\dfrac{y}{7}=\dfrac{12}{11}\Rightarrow y=\dfrac{7\cdot12}{11}=\dfrac{84}{11}\)
Mình làm mẫu 2 câu thôi nhé
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Câu 1:
( 2 + 4 + 6 + ... + 40 ) - x = 280
SSH là : ( 40 - 2 ) : 2 + 1 = 20 ( số )
Tổng là : ( 40 + 2 ) . 20 : 2 = 420
=> 420 - x = 280
=> x = 140
P/s : mk làm từng phần một nha
( x + 3 ) + ( x + 5 ) + ( x + 7 ) + ( x + 9 ) = 72
4x + 24 = 72
4x = 48
x = 12
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\(8+\left(x-6\right)=-40\)
\(\Leftrightarrow x-6=-40-8\)
\(\Leftrightarrow x-6=-48\)
\(\Leftrightarrow x=-48+6\)
\(\Leftrightarrow x=-42\)
\(\left(2x+5\right)-\left(-9\right)=-6\)
\(\Leftrightarrow2x+5=-6-9\)
\(\Leftrightarrow2x+5=-15\)
\(\Leftrightarrow2x=-15-5\)
\(\Leftrightarrow2x=-20\)
\(\Leftrightarrow x=\frac{-20}{2}\)
\(\Leftrightarrow x=-10\)
\(2\left(x-5\right)-3\left(x+7\right)=14\)
\(\Leftrightarrow2x-10-3x-21=14\)
\(\Leftrightarrow-x-31=14\)
\(\Leftrightarrow-x=14+31\)
\(\Leftrightarrow-x=45\)
\(\Leftrightarrow x=-45\)
\(-7\left(5-x\right)-2\left(x+3\right)=12\)
\(\Leftrightarrow-35+7x-2x-6=12\)
\(\Leftrightarrow-30x=12+6\)
\(\Leftrightarrow-30x=18\)
\(\Leftrightarrow x=\frac{-3}{5}\)
7x-2(2x+4)=40-x
=>7x-4x-8+x=40
=>4x=48
=>x=48/4=12
\(7x-2\left(2x+4\right)=40-x\)
\(\Leftrightarrow7x-4x-8=40-x\)
\(\Leftrightarrow7x-4x+x=40+8\)
\(\Leftrightarrow4x=48\)
\(\Leftrightarrow x=12\)