B=(1-\(\frac{1}{2}\))x(1-\(\frac{1}{3}\))x(1-\(\frac{1}{4}\))x...x(1-\(\frac{1}{20}\))
B=\(\frac{1}{2}\)X\(\frac{2}{3}\)X\(\frac{3}{4}\)X...X\(\frac{19}{20}\)
B=\(\frac{1.2.3.4.4.5.7.8.9.10.11.12.13.14.15.16.17.18.19}{2.3.4.5.6.7.8.9.10.11.12.13.14.15.16.17.18.19.20}\)
B=20
Vậy B=20
Không biết kết quả đúng ko nhưng cách làm thì đúng.
B= \(\left(1-\frac{1}{2}\right)x\left(1-\frac{1}{3}\right)x\left(1-\frac{1}{4}\right)x...x\left(1-\frac{1}{20}\right)\)
=\(\frac{1}{2}.\frac{2}{3}.\frac{3}{4}.....\frac{19}{20}\)(Rút gọn cả tử xuống mẫu )
= \(\frac{1.2.3...19}{2.3.4...20}\)
=\(\frac{1}{20}\)
Vậy B= \(\frac{1}{20}\)
\(B=\left(1-\frac{1}{2}\right)\left(1-\frac{1}{3}\right)...\left(1-\frac{1}{20}\right)\)
\(=\frac{1}{2}\cdot\frac{2}{3}\cdot...\cdot\frac{19}{20}\)
\(=\frac{1\cdot2\cdot...\cdot19}{2\cdot3\cdot...\cdot20}\)
\(=\frac{1}{20}\)
\(A=\frac{7}{4}\cdot\left(\frac{3333}{1212}+\frac{3333}{2020}+\frac{3333}{3030}+\frac{3333}{4242}\right)\)
\(=\frac{7}{4}\cdot\left[\frac{3333}{101}\cdot\left(\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}\right)\right]\)
\(=\frac{7}{4}\cdot\left[\frac{3333}{101}\cdot\left(\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}\right)\right]\)
\(=\frac{7}{4}\cdot\left[\frac{3333}{101}\cdot\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}\right)\right]\)
\(=\frac{7}{4}\cdot\left[\frac{3333}{101}\cdot\left(\frac{1}{3}-\frac{1}{7}\right)\right]\)
\(=\frac{7}{4}\cdot\left[\frac{3333}{101}\cdot\frac{4}{21}\right]\)
\(=\frac{7}{4}\cdot\frac{44}{7}\)
\(=11\)
B=(1-1/2)x(1-1/3)x(1-1/4)x...x(1-1/20)
=1.2.3...20/2.3.4...19
=1/20
nhớ cho một đúng nha
