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Tính $Afrac{1}{5times7}+frac{1}{7times9}+frac{1}{9times11}+...+frac{1}{87times89}$A15×7+17×9+19×11+...+187×89.
Đáp số: A
Đọc tiếp
Tính $A=\frac{1}{5\times7}+\frac{1}{7\times9}+\frac{1}{9\times11}+...+\frac{1}{87\times89}$.
| Đáp số: A = | |
Tính :
a) 3,5 x 2 + 1,25 x 4
b) \(\frac{3}{4}+2\times\left(\frac{1}{2}-\frac{1}{15}\right)\)
c) \(\frac{7}{11}\times\frac{1}{19}+\frac{7}{11}\times\frac{8}{19}-\frac{4}{11}\)
1) \(79\frac{19}{35}.\frac{7}{90}+15\frac{16}{35}.\frac{7}{90}\)
2)\(\left(3\frac{1}{5}-\frac{1}{11}\right).11\)
3)\(4\frac{1}{5}:\left(2\frac{1}{3}.1\frac{2}{5}\right)\)
4)\(13,2.\frac{15}{64}-\left(\frac{4}{5}+\frac{2}{3}\right):3\frac{2}{3}\)
So sánh \(A\)với\(13\),biết rằng:
\(A=\frac{13}{15}+\frac{7}{5}+\frac{3}{4}+\frac{1}{5}+\frac{1}{7}+\frac{19}{20}+\frac{5}{4}+\frac{1}{3}+\frac{1}{6}+\frac{1}{13}+\frac{17}{23}+\frac{9}{8}+\frac{2}{5}+\frac{1}{7}+\frac{1}{25}+\frac{3}{2}+\frac{1}{8}+\frac{1}{19}+\frac{1}{9}+\frac{1}{97}\)
Tìm a biết $frac{1}{3times7}+frac{1}{7times11}+frac{1}{11times15}+...+frac{1}{atimes(a+4)}frac{50}{609}$13×7+17×11+111×15+...+1a×(a+4)50609.
Đáp số: a
Đọc tiếp
Tìm a biết $\frac{1}{3\times7}+\frac{1}{7\times11}+\frac{1}{11\times15}+...+\frac{1}{a\times(a+4)}=\frac{50}{609}$.
Đáp số: a =
Tính :
a) ( 1 + 3 + 5 + 7 + ....... + 2007 + 2009 + 2011 ) x ( 125125 x 127 - 127127 x 125 )
b) \(\frac{1}{3}+\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}+\frac{1}{143}+\frac{1}{195}\)
2.Chứng minh A>1/2 ; còn B<1/2
A= \(\frac{7}{5\times7}+\frac{7}{7\times9}+...+\frac{7}{53\times55}\)
B= \(\frac{1}{3}+\frac{1}{15}+\frac{1}{35}+...+\frac{1}{99}\)
1, Tính :
a ) \(3\frac{17}{24}+2\frac{8}{15}+1\frac{7}{8}\)
b) \(2\frac{4}{11}+5\frac{2}{3}+\frac{7}{11}\)
1) Tính
a)\(\frac{13}{15}+\frac{13}{35}+\frac{13}{63}+\frac{13}{99}\)
b)\(\left(\frac{15}{1\cdot2\cdot3}+\frac{15}{2\cdot3\cdot4}+\frac{15}{3\cdot4\cdot5}+.....+\frac{15}{18\cdot19\cdot20}\right)\cdot x=1\)