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tổng quát: \(\frac{1}{n.\left(n+1\right)}=\frac{1}{n}-\frac{1}{n+1}\)
Ta có: \(\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}\)
\(=\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\)
\(=\frac{1}{3}-\frac{1}{10}=\frac{10}{30}-\frac{3}{30}=\frac{7}{30}\)
1.
\(\frac{3}{5}+\left\{\frac{2}{8}+\frac{2}{5}+\frac{6}{8}\right\}\)
\(=\frac{3}{5}+\left(\frac{10}{40}+\frac{36}{40}+\frac{30}{40}\right)\)
\(=\frac{3}{5}+\frac{76}{40}\)
\(=\frac{24}{40}+\frac{76}{40}\)
\(=\frac{100}{40}=\frac{5}{2}\)
2.
\(3\frac{2}{9}-\left\{1\frac{5}{8}+1\frac{2}{9}\right\}\)
\(=\frac{29}{9}-\left\{\frac{13}{8}+\frac{11}{9}\right\}\)
\(=\frac{29}{9}-\left\{\frac{117}{72}+\frac{88}{72}\right\}\)
\(=\frac{29}{9}-\frac{205}{72}\)
\(=\frac{232}{72}-\frac{205}{72}\)
Chúc cậu học tốt !!!
\(=\frac{27}{72}=\frac{3}{8}\)
\(1+1+2+3+4+5+5+6+7+8+9+9+9+7+5+5+6+9+9+9+9=128\)
Bạn tk mk nhé!! mk đang âm điểm qua trời
a] 4/12 ; 5/12 ; 11/2 ; 1/4
b] 1 ; 9/12; 12/5 ; 11/3
c] 8/21; 6/11;8/7
d] 2/3 ;2/7 15/2
a]1/3 5/12 11/2 1/4
b]1 3/4 12/5 33/9
c]8/21 6/11 8/7
d]2/3 2/7 15/2
1/10+2/9+3/8+4/7+5/6+1/6+3/7+5/8+7/9+9/10
=(1/10+9/10)+(2/9+7/9)+(3/8+5/8)+(4/7+3/7)+(5/6+1/6)
=1+1+1+1+1
=5
1/5 + 5/9 + 4/5 + 1/9 + 3/9
= ( 1/5 + 4/5 ) + ( 5/9 + 1/9 + 3/9 )
= 1 + 1
= 22
k cho mik nha
=107 nha
~HT~
K cho mình nha mn
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