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=2/10+3/10+4/10+......+13/10
=\(\frac{2+3+4+......+13}{10}\)
=90/10=9
k cho mình nha
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A=\(\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+...+\frac{1}{13}-\frac{1}{14}\)=\(\frac{1}{7}-\frac{1}{14}\)=\(\frac{1}{14}\)
B=0
\(\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}+\frac{1}{10.11}+\frac{1}{11.12}+\frac{1}{12.13}+\frac{1}{13.14}\)
\(=\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}+\frac{1}{10}-\frac{1}{11}+\frac{1}{11}-\frac{1}{12}+\frac{1}{12}-\frac{1}{13}+\frac{1}{13}-\frac{1}{14}\)
\(=\frac{1}{7}-\frac{1}{14}=\frac{1}{14}\)
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\(\frac{x+10}{90}+\frac{x+20}{80}+\frac{x+30}{70}+\frac{x+40}{60}+\frac{x+50}{50}=-5\)
<=> \(\frac{x+10}{90}+1+\frac{x+20}{80}+1+\frac{x+30}{70}+1+\frac{x+40}{60}+1+\frac{x+50}{50}+1=0\)
<=> \(\frac{x+100}{90}+\frac{x+100}{80}+\frac{x+100}{70}+\frac{x+100}{60}+\frac{x+100}{50}=0\)
<=> \(\left(x+100\right)\left(\frac{1}{90}+\frac{1}{80}+\frac{1}{70}+\frac{1}{60}+\frac{1}{50}\right)=0\)
<=> x + 100 = 0
<=> x = -100
Vậy x = -100
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\(M=\frac{15}{56}+\frac{1}{14}+\frac{1}{26}+\frac{5}{208}\)
\(M=\frac{15}{56}+\frac{4}{56}+\frac{8}{208}+\frac{5}{208}\)
\(M=\frac{19}{56}+\frac{13}{208}=\frac{45}{112}\)
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\(A=\frac{10^2}{20^2}+\frac{20^2}{30^2}=\frac{25}{36}\)
\(B=\frac{10^2+20^2}{20^2+30^2}=\frac{5}{13}\)
ta đổi :\(\frac{25}{36}\)và \(\frac{5}{13}\)ra thành cùng mẫu
suy ra bằng \(\frac{325}{468}\)và \(\frac{180}{468}\)
vì \(\frac{325}{468}>\frac{180}{468}\)nên \(A>B\)
đúng thì nhớ k đấy nhé
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