Chứng minh rằng: \(\frac{1}{5}+\frac{1}{13}+\frac{1}{25}+.....+\frac{1}{1985}< \frac{9}{20}\)

so sánh A= \(\frac{3^{2003}+5}{3^{2001}+5}\)và B= \(\frac{3^{2001}+1}{3^{1009}+1}\)

so sánh A= \(\frac{1}{1.1981}+\frac{1}{2.1982}+......+\frac{1}{24.2004}+\frac{1}{25.2005}\)

B =\(\frac{1}{1.61}+\frac{1}{2.27}+.....+\frac{1}{1979.2004}+\frac{1}{1980.2005}\)

Các bn lm giúp mk nhé (dấu . là dấu x nhé )

1. Tính

a)\(\frac{\left(1+2+3+...+100\right).\left(\frac{1}{3}-\frac{1}{5}-\frac{1}{7}-\frac{1}{9}\right).\left(6,3.12-21.3,6\right)}{\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+\frac{1}{100}}\)

b) \(\frac{1}{100.99}-\frac{1}{99.98}-\frac{1}{98.98}-...-\frac{1}{3.2}-\frac{1}{2.1}\)

2. Tìm số hữu tỉ x, biết rằng:

a) \(\frac{x+1}{10}+\frac{x+1}{11}+\frac{x+1}{12}=\frac{x+1}{13}+\frac{x+1}{14}\)

b)\(\frac{x+4}{2000}+\frac{x+3}{2001}=\frac{x+2}{2002}+\frac{x+1}{2003}\)

CÁC BẠN GIẢI GIÚP MK NHA, AI LÀM NHANH VÀ ĐÚNG MK TICK CHO -.-

các bn làm giúp mk vs thông cảm nha:(đều là hs nên hiểu nhau cả mà,ai làm đc câu nào thì cố giúp mk nha)

a)\(-66\left(\frac{1}{2}-\frac{1}{3}-\frac{1}{11}\right)+124\left(-37\right)+63.\left(-124\right)\)

b)\(\left(2-\frac{3}{2}\right).\left(2-\frac{4}{3}\right).\left(2-\frac{5}{4}\right).\left(2-\frac{6}{5}\right)\)

c)\(\frac{0,75-0,6+\frac{3}{7}+\frac{3}{13}}{2,75-2,2+\frac{11}{7}+\frac{11}{13}}\)

d)\(\left[\left(\frac{2}{193}-\frac{3}{386}\right).\frac{193}{7}+\frac{33}{34}\right]:\left[\left(\frac{7}{2001}+\frac{11}{4002}\right).\frac{2001}{25}+\frac{9}{2}\right]\)

e)\(\frac{\left(13\frac{1}{4}-2\frac{5}{27}-10\frac{5}{6}\right).230\frac{1}{25}+46\frac{3}{4}}{\left(1\frac{2}{7}+\frac{10}{3}\right).\left(12\frac{1}{3}-14\frac{2}{7}\right)}\)

tìm phần nguyên

\(A=\left(\frac{-5}{11}\right).\frac{7}{15}+\frac{11}{-5}.\frac{30}{33}\)

\(B=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+....+\frac{1}{x.\left(x+1\right)}\)(x∈Z)

\(C=\frac{1}{3}-\frac{3}{5}+\frac{5}{7}-\frac{7}{9}+\frac{9}{11}-\frac{11}{13}+\frac{11}{13}-\frac{9}{11}+\frac{7}{9}-\frac{5}{7}+\frac{3}{5}-\frac{1}{3}\)

\(D=\frac{1}{3}-\left[\left(-\frac{5}{4}\right)-\left(\frac{1}{4}+\frac{3}{8}\right)\right]\)

giúp mk nhé, mk tk, mk thanks nhiều

các bn làm giúp mk vs thông cảm nha:(đều là hs nên hiểu nhau cả mà,ai làm đc câu nào thì cố giúp mk nha)

a)\(-66\left(\frac{1}{2}-\frac{1}{3}-\frac{1}{11}\right)+124.\left(-37\right)+61.\left(-124\right)\)

b)\(\left(2-\frac{3}{2}\right).\left(2-\frac{4}{3}\right).\left(2-\frac{5}{4}\right).\left(2-\frac{6}{5}\right)\)

c)\(\frac{0,75-0,6+\frac{3}{7}+\frac{3}{11}}{2,75-2,2+\frac{11}{7}+\frac{11}{13}}\)

d)\(\left[\left(\frac{2}{193}-\frac{3}{386}\right).\frac{193}{7}+\frac{33}{34}\right]:\left[\left(\frac{7}{2001}+\frac{11}{4002}\right).\frac{2001}{25}+\frac{9}{2}\right]\)

e)\(\frac{\left(13\frac{1}{4}-2\frac{5}{21}-10\frac{5}{6}\right).230\frac{1}{5}+46\frac{3}{4}}{\left(1\frac{2}{7}+\frac{10}{3}\right).\left(12\frac{1}{3}-14\frac{2}{7}\right)}\)