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3:
\(=\dfrac{1}{7}\cdot\dfrac{3}{5}\cdot\dfrac{5}{6}\cdot\dfrac{5}{8}=\dfrac{1}{7}\cdot\dfrac{1}{2}\cdot\dfrac{5}{8}=\dfrac{5}{112}\)
4:
=>2/3:x=-2-1/3=-7/3
=>x=-2/3:7/3=-2/7
5:
AC=CB=12/2=6cm
IB=6/2=3cm
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Bài 5 :
S = 1 + 3 - 5 - 7 + 9 + 11 - ... - 397 - 399
S = 1 + (3 - 5 - 7 + 9) + (11 - 13 - 15 + 17) + ... + (387 - 389 - 391 + 393) + (395 - 397 - 399)
S = 1 + 0 + 0 + ... + 0 + (- 401)
S = 1 - 401
S = - 400
Bài 5
A= 1+3-5-7+9+11-13-15+...-397-399
A= ( 1+3-5-7)+( 9+11-13-15)+...+( 393+395-397-399)
A= -8 -8 -...-8
A = -8.50 ( từ 1 đến 399 có 200 số, chia làm 4 cặp)
A= -400
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b; 2\(^x\) = 4.128
2\(^x\) = 512
2\(^x\) = 29
\(x\) = 9
Vậy \(x\) = 9
c; 2\(^x\).3\(^x\) = 4.9
6\(^x\) = 36
6\(^x\) = 62
\(x=2\)
Vậy \(x=2\)
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\(=\frac{4+9}{4.9}-\frac{14-9}{9.14}-\frac{14+19}{14.19}+\frac{19+24}{19.24}\)
\(=\frac{4}{4.9}+\frac{9}{4.9}-\frac{14}{9.14}-\frac{9}{9.14}-\frac{14}{14.19}+\frac{19}{14.19}+\frac{19}{19.24}+\frac{24}{19.24}\)
\(\frac{1}{9}+\frac{1}{4}-\frac{1}{9}-\frac{1}{14}-\frac{1}{19}+\frac{1}{14}+\frac{1}{19}+\frac{1}{24}\)
\(=\frac{1}{4}+\frac{1}{24}=\frac{7}{24}\)
AI THẤY ĐÚNG ỦNG HỘ NHA
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\(2x+3=8\)
\(\Rightarrow2x=8-3\)
\(\Rightarrow2x=5\)
\(\Rightarrow x=\dfrac{5}{2}\)
\(x:5-2=3\)
\(\Rightarrow x:5=3+2\)
\(\Rightarrow x:5=5\)
\(\Rightarrow x=5\cdot5\)
\(\Rightarrow x=25\)
\(x:7-2=19\)
\(\Rightarrow x:7=19+2\)
\(\Rightarrow x:7=21\)
\(\Rightarrow x=21\cdot7\)
\(\Rightarrow x=147\)
Mình chưa rõ đề
\(20-\left(x+3\right)=5\)
\(\Rightarrow-x-3=5-20\)
\(\Rightarrow-x-3=-15\)
\(\Rightarrow-x=-15+3\)
\(\Rightarrow-x=-12\)
\(\Rightarrow x=12\)
\(\frac{2}{x}+\frac{5}{4.9}+...+\frac{5}{99.104}=\frac{19}{52}\)
\(\Rightarrow\frac{2}{x}+\left(\frac{1}{4}-\frac{1}{9}+...+\frac{1}{99}-\frac{1}{104}\right)=\frac{19}{52}\)
\(\Rightarrow\frac{2}{x}+\left(\frac{1}{4}-\frac{1}{104}\right)=\frac{19}{52}\Rightarrow\frac{2}{x}+\frac{25}{104}=\frac{19}{52}\)
\(\frac{2}{x}=\frac{38}{104}-\frac{25}{104}=\frac{13}{104}\Rightarrow x=2:\frac{13}{104}=2.\frac{104}{13}=16\Rightarrow x=16\)
\(\frac{2}{x}+\frac{5}{4.9}+\frac{5}{9.14}+......+\frac{5}{99.104}=\frac{19}{52}\)
\(\frac{2}{x}+\frac{1}{4}-\frac{1}{9}+\frac{1}{9}-\frac{1}{14}+.......+\frac{1}{99}-\frac{1}{104}=\frac{19}{52}\)
\(\frac{2}{x}+\left(\frac{1}{4}-\frac{1}{104}\right)=\frac{19}{52}\)
\(\frac{2}{x}+\frac{25}{104}=\frac{19}{52}\)
\(\frac{2}{x}=\frac{19}{52}-\frac{25}{104}\)
\(\frac{2}{x}=\frac{13}{104}\)
\(\Rightarrow13x=2.104=208\)
\(\Rightarrow x=208:13=16\)
Vậy \(x=16\)