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DX
19 tháng 5 2021 lúc 18:12
Cho \(S=\dfrac{1}{31}+\dfrac{1}{32}+\dfrac{1}{33}+...+\dfrac{1}{60}\) .
Chứng minh rằng \(3< 5S< 4\)
Bài 1: tính
Cho A dfrac{1}{31}+dfrac{1}{32}+dfrac{1}{33}+........+dfrac{1}{60}dfrac{7}{12}
Bdfrac{1}{3^2}+dfrac{1}{3^2}+dfrac{1}{5^2}+.....+dfrac{1}{50^2}
CMR B dfrac{1}{4}; B dfrac{4}{9}
C dfrac{1}{2}.dfrac{3}{4}.dfrac{5}{6}.dfrac{7}{8}...........dfrac{79}{80}dfrac{1}{9}
Đọc tiếp
Bài 1: tính
Cho A= \(\dfrac{1}{31}+\dfrac{1}{32}+\dfrac{1}{33}+........+\dfrac{1}{60}>\dfrac{7}{12}\)
B=\(\dfrac{1}{3^2}+\dfrac{1}{3^2}+\dfrac{1}{5^2}+.....+\dfrac{1}{50^2}\)
CMR B > \(\dfrac{1}{4}\); B < \(\dfrac{4}{9}\)
C = \(\dfrac{1}{2}.\dfrac{3}{4}.\dfrac{5}{6}.\dfrac{7}{8}...........\dfrac{79}{80}\)<\(\dfrac{1}{9}\)
Tìm \(x\)
1. \(\dfrac{1}{7}=\dfrac{8}{-x}\)
2. \(\dfrac{3x}{9}=\dfrac{2}{6}\)
3. \(4\dfrac{2}{5}:\left(\dfrac{-33}{10}\right)+x=-1\dfrac{5}{6}\)
4. \(45\%.x-2\dfrac{3}{8}=-1\dfrac{31}{40}\)
5. \(\left(x-2\dfrac{1}{4}\right):\left(-\dfrac{5}{6}\right)=3\)
DX
2 tháng 2 2021 lúc 12:48
a)Rút gọn phân số : \(\dfrac{25^{28}+25^{24}+25^{20}+.....+25^4+1}{25^{30}+25^{28}+....+25^2+1}\)
b) Cho S = 1-3 + 32-33+.....+398-399
1. Tìm x,y thuộc Z , biết :
( x - 2 ) . ( 2y + 1 ) = 9
2. Cho A = 3 + 32 + 33 + ... + 3150
CM : A chia hết cho 4 ; A chia hết cho 12
Hết , ahihi ☺☛⚽
thực hiện phép tính.
a) b) C= 3+31+32+33+...+3100 c)\(\dfrac{2018.2019-1}{2018^2+2017}\)
\(\dfrac{2^{10}.13+2^{10}.65}{2^8.104}\)
1 So sánh
a) dfrac{51}{56}vàdfrac{61}{66}
b)dfrac{41}{43}vàdfrac{172}{165}
c)dfrac{101}{506}vàdfrac{-707}{3534}
d) dfrac{-43}{119}vàdfrac{41}{117}
2 Rút gọn và quy đồng
a)dfrac{125}{1000};dfrac{198}{126};dfrac{3}{243};dfrac{103}{3009}
b)dfrac{1}{2};dfrac{1}{3};dfrac{1}{38};dfrac{-1}{12}
c)dfrac{9}{30};dfrac{90}{8};dfrac{15}{1000}
3 So sánh
a)dfrac{-3}{5}vàdfrac{39}{65}
b)dfrac{-9}{27}vàdfrac{11}{123}
c) dfrac{-3}{4}vàdfrac{4}{-5}
d)dfrac{2}{-3}vàdfrac{5}{7}
Đọc tiếp
1 So sánh
a) \(\dfrac{51}{56}và\dfrac{61}{66}\)
b)\(\dfrac{41}{43}và\dfrac{172}{165}\)
c)\(\dfrac{101}{506}và\dfrac{-707}{3534}\)
d) \(\dfrac{-43}{119}và\dfrac{41}{117}\)
2 Rút gọn và quy đồng
a)\(\dfrac{125}{1000};\dfrac{198}{126};\dfrac{3}{243};\dfrac{103}{3009}\)
b)\(\dfrac{1}{2};\dfrac{1}{3};\dfrac{1}{38};\dfrac{-1}{12}\)
c)\(\dfrac{9}{30};\dfrac{90}{8};\dfrac{15}{1000}\)
3 So sánh
a)\(\dfrac{-3}{5}và\dfrac{39}{65}\)
b)\(\dfrac{-9}{27}và\dfrac{11}{123}\)
c) \(\dfrac{-3}{4}và\dfrac{4}{-5}\)
d)\(\dfrac{2}{-3}và\dfrac{5}{7}\)
NC
8 tháng 5 2021 lúc 11:11
Tìm x, biết:
a) \(\dfrac{3}{4.7}+\dfrac{3}{7.10}+....+\dfrac{3}{x\left(x+3\right)}=\dfrac{9}{38}\)
b) \(\dfrac{1}{21}+\dfrac{1}{28}+\dfrac{1}{36}+...+\dfrac{2}{x\left(x+1\right)}=\dfrac{2}{9}\)
cho S = 1/31+1/32+1/33+...+1/59+1/60. cmr 3/4<S<4/5