2x -270 x 5 =430
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Chọn A
4 phút = 60 giây × 4 = 240 giây
4 phút 30 giây = 240 giây + 30 giây = 270 giây
\(1,\\ \left(x-7\right)^{x+1}-\left(x-7\right)^{x+11}=0\\ \Leftrightarrow\left(x-7\right)^{x+1}\left[1-\left(x-7\right)^{10}\right]=0\\ \Leftrightarrow\left[{}\begin{matrix}\left(x-7\right)^{x+1}=0\\\left(x-7\right)^{10}=1\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x-7=0\\x-7=1\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=7\\x=8\end{matrix}\right.\)
\(2,\\ a,\left|2x-3\right|>5\Leftrightarrow\left[{}\begin{matrix}2x-3< -5\\2x-3>5\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x< -1\\x>4\end{matrix}\right.\\ b,\left|3x-1\right|\le7\Leftrightarrow\left[{}\begin{matrix}3x-1\le7\\1-3x\le7\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x\le\dfrac{8}{3}\\x\ge-2\end{matrix}\right.\\ c,\cdot x< -\dfrac{3}{2}\\ \Leftrightarrow5-3x+\left(-2x-3\right)=7\Leftrightarrow2-5x=7\Leftrightarrow x=-1\left(ktm\right)\\ \cdot-\dfrac{3}{2}\le x\le\dfrac{5}{3}\\ \Leftrightarrow\left(5-3x\right)+\left(2x+3\right)=7\Leftrightarrow8-x=7\Leftrightarrow x=1\left(tm\right)\\ \cdot x>\dfrac{5}{3}\\ \Leftrightarrow\left(3x-5\right)+\left(2x+3\right)=7\Leftrightarrow5x-2=7\Leftrightarrow x=\dfrac{9}{5}\left(tm\right)\\ \Leftrightarrow S=\left\{1;\dfrac{9}{5}\right\}\)
\(3^{x+4}+3^{x+2}=270\Rightarrow3^{x+2}\left(3^2+1\right)\)\(=270\Rightarrow3^{x+2}\cdot10=270\)\(=>3^{x+2}=270:10=27=>x=1\)
Ta có:
\(\dfrac{x}{10}=\dfrac{y}{5}\Rightarrow\dfrac{x}{20}=\dfrac{y}{10}\) (1)
\(\dfrac{y}{2}=\dfrac{z}{3}\Rightarrow\dfrac{y}{10}=\dfrac{z}{25}\) (2)
Từ (1) và (2) \(\Rightarrow\dfrac{x}{20}=\dfrac{y}{10}=\dfrac{z}{25}\)
Áp dụng tính chất dãy số bằng nhau ta có:
\(\dfrac{x}{20}=\dfrac{y}{10}=\dfrac{z}{25}=\dfrac{2x-y+4z}{2\cdot20-10+4\cdot25}=\dfrac{270}{130}=\dfrac{27}{13}\)
\(\Rightarrow\dfrac{x}{20}=\dfrac{27}{13}\Rightarrow x=\dfrac{540}{13}\)
\(\Rightarrow\dfrac{y}{10}=\dfrac{27}{13}\Rightarrow y=\dfrac{270}{13}\)
\(\Rightarrow\dfrac{z}{25}=\dfrac{27}{13}=\dfrac{675}{13}\)
Có: \(\dfrac{x}{10}=\dfrac{y}{5}\Leftrightarrow\dfrac{x}{10}=\dfrac{2y}{10}\left(1\right)\)
\(\dfrac{y}{2}=\dfrac{z}{3}\Leftrightarrow\dfrac{2y}{10}=\dfrac{2z}{15}\left(2\right)\)
Từ (1) và (2) => \(\dfrac{x}{10}=\dfrac{2y}{10}=\dfrac{2z}{15}\)=> \(\dfrac{x}{10}=\dfrac{y}{5}=\dfrac{2z}{15}\)
Áp dung tính chất của dãy tỉ số bằng nhau và 2x - y + 4z = 270, ta có:
\(\dfrac{x}{10}=\dfrac{y}{5}=\dfrac{2z}{15}=\dfrac{2x}{20}=\dfrac{4z}{30}=\dfrac{2x-y+4z}{20-5+30}=\dfrac{270}{45}=6\)
\(\Rightarrow\left\{{}\begin{matrix}\dfrac{x}{10}=6\\\dfrac{y}{5}=6\\\dfrac{2z}{15}=6\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}x=60\\y=30\\z=45\end{matrix}\right.\)
Vậy...
(190-2x):25=270
190-2x =270.25
190-2x =6750
2x =6750-190
2x = 6560
x = 6560/2=3280
720:[41-(2x-5)]=2^3.5
720:[41-(2x-5)]=40
41-(2x-5)=720/40
41-(2x-5)= 18
2x-5 = 41-18
2x-5 = 23
2x = 23+5
2x = 28
x = 28/2=14
Còn bài 3 thì mình chịu
a, 7\(x\) - \(x\) = 521 : 519 + 3.22.7
6\(x\) = 53 + 3.4.7
6\(x\) = 125 + 12.7
6\(x\) = 125 + 84
6\(x\) = 209
\(x\) = 209 : 6
\(x\) = \(\dfrac{209}{6}\)
b; 11\(x\) - 7\(x\) + 34 : 33 = 54 + 2\(x\)
4\(x\) + 3 = 625 + 2\(x\)
4\(x\) - 2\(x\) = 625 - 3
2\(x\) = 622
\(x\) = 622 : 2
\(x\) = 311
c; 75 - 5.(\(x-3\))3 = 700
5.(\(x\) - 3)3 = 700 - 75
5.(\(x\) - 3)3 = - 625
(\(x\) - 30)3 = - 625 : 5
(\(x\) - 30)3 = - 125
(\(x-3\))3 = (-5)3
\(x\) - 3 = - 5
\(x\) = - 5 + 3
\(x\) = -2
d, 3.(2\(x\) - 1)2 = 75
(2\(x\) - 1)2 = 75 : 3
(2\(x\) - 1)2 = 25
\(\left[{}\begin{matrix}2x-1=-5\\2x-1=5\end{matrix}\right.\)
\(\left[{}\begin{matrix}2x=-5+1\\2x=5+1\end{matrix}\right.\)
\(\left[{}\begin{matrix}2x=-4\\2x=6\end{matrix}\right.\)
\(\left[{}\begin{matrix}x=-2\\x=3\end{matrix}\right.\)
a)\(280-\left(x-140\right):35=270\)
\(\Leftrightarrow\left(x-140\right):35=10\)
\(\Leftrightarrow x-140=350\)
\(\Leftrightarrow x=490\)
b) \(\left(190-2x\right):35-32=16\)
\(\Leftrightarrow\left(190-2x\right):35=48\)
\(\Leftrightarrow190-2x=1680\)
\(\Leftrightarrow2x=-1490\Leftrightarrow x=-745\)
c) \(720:\left[41-\left(2x-5\right)\right]=2^3.5\)
\(\Leftrightarrow720:\left[41-\left(2x-5\right)\right]=40\)
\(\Leftrightarrow41-\left(2x-5\right)=18\)
\(\Leftrightarrow2x-5=23\)
\(\Leftrightarrow2x=28\Leftrightarrow x=14\)
280-(x-140):35=270
(x-140):35=280-270
(x-140):35=10
(x-140)=10×35
(x-140)=350
x=350-140
x=210
vậy x=210
(192-2x):35-32=16
(192-2x):35=16+32
(192-2x):35=48
(192-2x)=48×35
(192-2x)=1680
2x=192-1680
2x=-1488
x=-1488:2
x=-744
vậy x=-744
2x - 270 × 5 = 430
2x - 1350 = 430
2x = 1780
X= 890
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Chúc bạn học tốt
2\(x\)- 270 x 5 = 430
2\(x\) = 430 + (270 : 5)
2\(x\) = 430 + 54
2\(x\) = 484
\(x\) = 484 : 2
\(x\) = 242
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