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\(E=\frac{100}{1}+\frac{1}{100}+\frac{99}{2}+\frac{2}{99}+...+\frac{51}{50}+\frac{50}{51}\)

\(E=\left(\frac{99}{2}+1\right)+\left(\frac{98}{3}+1\right)+...+\left(\frac{50}{51}+1\right)+1\)

\(E=\frac{101}{2}+\frac{101}{3}+...+\frac{101}{101}\)

\(E=101.\left(\frac{1}{2}+\frac{1}{3}+..+\frac{1}{101}\right)\)

Đến đây chắc tự hiểu

\(2-\left|\frac{3}{4}-x\right|=\frac{7}{12}=\left|\frac{3}{4}-x\right|=2-\frac{7}{12}\Rightarrow\left|\frac{3}{4}-x\right|=\frac{17}{12}\Rightarrow\begin{cases}\frac{3}{4}-x=\frac{17}{12}\\\frac{3}{4}-x=-\frac{17}{12}\end{cases}\Rightarrow\begin{cases}x=\frac{-2}{3}\\\frac{13}{6}\end{cases}}\)

 ChữKiệt ღ ๖ۣۜLý๖ۣۜ đẹp mà

M=2/3.5+2/5.7+...+2/97.99

M=1.(1/3-1/5+...+1/97-1/99)

M=1.(1/3-1/99)

M=32/99

M=2/3.5+2/5.7+2/7.9+....+2/97.99

M=1.(1/3-1/5+1/5-1/7+...+1/97-1/99)

M=1.(1/3-1/99)

M=32/99

1/1.3+1/3.5+...+1/2013.2015

=1/2.(1/1-1/3+1/3-1/5+...+1/2013-1/2015)

=1/2.(1/1-1/2015)

=1/2.2014/2015

=1007/2015

Đề đúng: 1/2+5/6+11/12+19/20+29/30+41/42+55/56+71/72+89/90 chứ nếu thế để mk làm cho :

1/2+5/6+11/12+19/20+29/30+41/42+55/56+71/72+89/90=

1-1/2+1-1/6+1-1/12+1-1/20+1-1/30+1-1/42+1-1/56+1-1/72+1-1/90 =

9 – (1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90) =

9 – [1/(1x2)+1/(2x3)+1/(3x4)+1/(4x5)+1/(5x6)+1/(6x7)+1/(7x8)+1/(8x9)+1/(9x10)] =

9 – ( 1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10) =

9 – (1 – 1/10) = 9 – 9/10 = 81/10

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