A=\(\frac{1.2.3.4...8.9}{2.3.4.5...9.10}\)

A=\(\frac{1}{10}\)

mình làm đc 1 câu thôi. Bạn thông cảm nhé

\(C=\frac{3.8.15....80.99}{4.9.16.81.100}\)

\(=\frac{1.3.2.4.3.5...8.10.9.11}{2.2.3.3.4.4...9.9.10.10}\)

\(=\frac{\left(1.2.3....9\right).\left(3.4.5...10.11\right)}{\left(2.3.4.5...10\right).\left(2.3.4...10\right)}\)

\(=\frac{11}{10}\)

trả lời 

c=\(\frac{3}{4}\cdot\frac{8}{9}\cdot\frac{15}{16}\cdot....\cdot\frac{99}{100}\)

C=\(\frac{3.8.15....99}{4.9.16.100}\)

C=\(\frac{1.3.2.4.3.5.....9.11}{2.2.3.3.4.4....10.10}\)

C=\(\frac{\left(1.2.....9\right)}{2.3....10}.\left(\frac{3.4....11}{2.3...10}\right)\)

C=\(\frac{1}{10}\cdot\frac{11}{2}=\frac{11}{20}\)

làm ẩu quá

đoạn cuối \(=\frac{11}{20}\)nha sorry

bn lê trung hiếu làm đúng rồi !

a) \(\left(\frac{11}{4}.\frac{-5}{9}-\frac{4}{9}.\frac{11}{4}\right).\frac{8}{33}\)

=\(\frac{11}{4}\left(-\frac{5}{9}-\frac{4}{9}\right).\frac{8}{33}\)

=\(\frac{11}{4}\cdot-1\cdot\frac{8}{33}\)

=\(-\frac{11}{4}\cdot\frac{8}{33}\)

=\(-\frac{2}{3}\)

b)\(-\frac{1}{4}\cdot\frac{152}{11}+\frac{68}{4}\cdot-\frac{1}{11}\)

=\(\frac{-1.152}{4.11}+\frac{68}{4}\cdot\frac{-1}{11}\)

=\(\frac{-1.152}{11.4}+\frac{68}{4}\cdot\frac{-1}{11}\)

=\(\frac{-1}{11}\cdot\frac{152}{4}+\frac{68}{4}\cdot\frac{-1}{11}\)

=\(\frac{-1}{11}\cdot\left(\frac{152}{4}+\frac{68}{4}\right)\)

=\(\frac{-1}{11}\cdot55=-5\)

c)\(\frac{-2}{3}\cdot\frac{4}{5}+\frac{2}{3}\cdot\frac{3}{5}\)

=\(-1\cdot\frac{2}{3}\left(\frac{4}{5}+\frac{3}{5}\right)\)

=\(-1\cdot\frac{2}{3}\cdot\frac{7}{5}\)

=\(-\frac{2}{3}\cdot\frac{7}{5}\)

=\(\frac{-14}{15}\)

d) chưa nghĩ ra nhé

e) bạn chép sai đề bài rồi

mk mới kiểm tra 45 phút nên biết

đề bài nè

\(\frac{3}{2^2}\cdot\frac{8}{3^2}\cdot\frac{15}{4^2}\cdot...\cdot\frac{899}{30^2}\)

=\(\frac{1.3}{2^2}\cdot\frac{2.4}{3^2}\cdot\frac{3.5}{4^2}\cdot...\cdot\frac{29.31}{30^2}\)

=\(\frac{1.3.2.4.3.5...29.31}{2.2.3^2.4^2...30.30}\)

=\(\frac{1.2.3^2.4^2.5^2....29^2.30.31}{2.2.3^2.4^2.5^2....29^2.30.30}\)

=\(\frac{1.31}{2.30}\)

=\(\frac{31}{60}\)

a)trong ngoac bn dat thau so chung la 11/4 rui tinh binh thuong                                                                         b)bn tu lam nhe                                                                                                                                             c)dat thua so chung                                                                                                                                       d)tinh trong ngoac ra rui nhan vs                                                                                                                       e) mk bo tay 

thanks mấy pn nha

\(P=\frac{1}{2}.\frac{3}{4}.\frac{4}{5}.\frac{5}{6}......\frac{399}{400}\)

\(P=\frac{1.3.4.5....399}{2.4.5.6.....400}\)

\(P=\frac{1.3}{2.400}\)

\(P=\frac{3}{800}\)

Vì \(\frac{3}{800}< \frac{40}{800}\)

\(\Rightarrow P< \frac{40}{800}\)

\(\Rightarrow P< \frac{1}{20}\left(đpcm\right)\)

Ta co:

\(P=\frac{1}{2}.\frac{3.4.5...399}{4.5.6...400}\)

\(\Leftrightarrow P=\frac{1}{2}.\frac{3}{400}=\frac{3}{800}< \frac{3}{600}=\frac{1}{20}\)

\(\Rightarrow P< \frac{1}{20}\left(dpcm\right).\)

\(P=\frac{1}{2}.\frac{3}{4}.\frac{4}{5}.\frac{5}{6}......\frac{399}{400}\)

\(P=\frac{1.3.4.5.....399}{2.4.5.6....400}\)

\(P=\frac{1.3}{2.400}\)

\(P=\frac{3}{800}\)

\(V\text{ì}\frac{3}{800}< \frac{40}{800}\)

\(\Rightarrow P< \frac{40}{800}\)

\(\Rightarrow P< \frac{1}{20}\left(\text{đ}pcm\right)\)