đề sai rồi

đề sai rồi

\(A=\frac{1}{2.3}+\frac{1}{6.5}+\frac{1}{10.7}+...+\frac{1}{198.101}\)

\(A=2.\left(\frac{1}{2.6}+\frac{1}{6.10}+\frac{1}{10.14}+...+\frac{1}{198.202}\right)\)

\(A=2.\frac{1}{4}.\left(\frac{1}{2}-\frac{1}{6}+\frac{1}{6}-\frac{1}{10}+\frac{1}{10}-\frac{1}{14}+...+\frac{1}{198}-\frac{1}{202}\right)\)

\(A=\frac{1}{2}.\left(\frac{1}{2}-\frac{1}{202}\right)\)

\(A=\frac{1}{2}.\frac{50}{201}\)

\(A=\frac{25}{101}\)

=25/101

k cho to nhe

\(A=\frac{1}{2.3}+\frac{1}{6.5}+\frac{1}{10.7}+...+\frac{1}{198.101}\)

\(A=2.\left(\frac{1}{2.6}+\frac{1}{6.10}+\frac{1}{10.14}+...+\frac{1}{198.202}\right)\)

\(A=2.\frac{1}{4}.\left(\frac{1}{2}-\frac{1}{6}+\frac{1}{6}-\frac{1}{10}+\frac{1}{10}-\frac{1}{14}+...+\frac{1}{198}-\frac{1}{202}\right)\)

\(A=\frac{1}{2}.\left(\frac{1}{2}-\frac{1}{202}\right)\)

\(A=\frac{1}{2}.\frac{50}{201}\)

\(A=\frac{25}{101}\)

\(A=\frac{1}{2.3}+\frac{1}{6.5}+\frac{1}{14.9}+...+\frac{1}{198.101}\)

\(A=\frac{1}{2}\left(\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+...+\frac{1}{99.101}\right)\)

Ta thấy : thừa số thứ nhất ở mẫu của phân số liền sau = thừa số thứ nhất của phân số liền trước + 4

Thừa số thứ hai ở mẫu của phân số liền sau = thừa số thứ hai của phân số liền trước + 2 

\(4A=\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{99.101}\)

\(4A=\frac{3-1}{1.3}+\frac{5-3}{3.5}+\frac{7-5}{5.7}+\frac{9-7}{7.9}+...+\frac{101-99}{99.101}\)

4A= \(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{99}-\frac{1}{101}=1-\frac{1}{101}=\frac{100}{101}\)

\(A=\frac{100}{101.4}=\frac{25}{101}\)

\(A=\frac{1}{2.3}+\frac{1}{6.5}+\frac{1}{10.7}+...+\frac{1}{198.101}\)

\(A=2\times\left(\frac{1}{2.6}+\frac{1}{6.10}+\frac{1}{10.14}+...+\frac{1}{198.202}\right)\)

\(A=2\times\frac{1}{4}\times\left(\frac{1}{2}-\frac{1}{6}+\frac{1}{6}-\frac{1}{10}+\frac{1}{10}-\frac{1}{14}+...+\frac{1}{198}-\frac{1}{202}\right)\)

\(A=\frac{1}{2}\times\left(\frac{1}{2}-\frac{1}{202}\right)\)

\(A=\frac{1}{2}\times\frac{50}{101}\)

\(A=\frac{25}{101}\)

1/2A=1/2*3*2+1/6*5*2+1/10*7*2+...+1/198*101*2

1/2A=1/2*6+1/6*10+1/10*14+...+1/198*202

4/2A=4/2*6+4/6*10+4/10*14+...+4/198*202

2A=1/2-1/6+1/6-1/10+1/10-1/14+...+1/198-1/202

2A=1/2-1/202

2A=100/202

A=50/202

\(A=\frac{1}{2.3}+\frac{1}{6.5}+\frac{1}{10.7}+...+\frac{1}{198.101}\)

\(A=2.\left(\frac{1}{2.6}+\frac{1}{6.10}+\frac{1}{10.14}+...+\frac{1}{198.202}\right)\)

\(A=2.\frac{1}{4}.\left(\frac{1}{2}-\frac{1}{6}+\frac{1}{6}-\frac{1}{10}+\frac{1}{10}-\frac{1}{14}+...+\frac{1}{198}-\frac{1}{202}\right)\)

\(A=\frac{1}{2}.\left(\frac{1}{2}-\frac{1}{202}\right)\)

\(A=\frac{1}{2}.\frac{50}{201}\)

\(A=\frac{25}{101}\)

\(A=\frac{1}{2.3}+\frac{1}{6.5}+\frac{1}{10.7}+...+\frac{1}{198.101}\)

\(A=2.\left(\frac{1}{2.6}+\frac{1}{6.10}+\frac{1}{10.14}+...+\frac{1}{198.202}\right)\)

\(A=2.\frac{1}{4}.\left(\frac{1}{2}-\frac{1}{6}+\frac{1}{6}-\frac{1}{10}+\frac{1}{10}-\frac{1}{14}+...+\frac{1}{198}-\frac{1}{202}\right)\)

\(A=\frac{1}{2}.\left(\frac{1}{2}-\frac{1}{202}\right)\)

\(A=\frac{1}{2}.\frac{50}{201}\)

\(A=\frac{25}{101}\)

 Như bạn kia là rất đúng 

\(A=\frac{1}{2.3}+\frac{1}{6.5}+\frac{1}{10.7}+...+\frac{1}{198.101}\)

\(A=\frac{1}{2}\left(\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+...+\frac{1}{99.101}\right)\)

\(4A=\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{99.101}\)

\(4A=\frac{3-1}{1.3}+\frac{5-3}{3.5}+\frac{7-5}{5.7}+...+\frac{101-99}{99.101}\)

\(4A=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-...-\frac{1}{99}+\frac{1}{99}-\frac{1}{101}\)

\(4A=1-\frac{1}{101}=\frac{100}{101}\)

\(A=\frac{100}{101.4}=\frac{25}{101}\)

\(A=\frac{1}{2.3}+\frac{1}{6.5}+\frac{1}{10.7}+\frac{1}{14.9}+...+\frac{1}{198.101}\)

\(A=\frac{1}{2}\left(\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+...+\frac{1}{99.101}\right)\)

\(4A=\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{99.101}\)

\(4A=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{99}-\frac{1}{101}\)

\(4A=1-\frac{1}{101}=\frac{100}{101}\)

\(A=\frac{100}{101}:4=\frac{25}{101}\)

đáp số 

25/101

hok tốt

tất cả rút \(\frac{1}{2}\) ra ngoài ta có :

\(\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+...+\frac{1}{99.101}\)

đến đây thì dễ rồi tự làm tiếp đi , ko hiểu thì hỏi nha

cái này bn đặt làm hiệu sẽ ra ngay thôi!

1/2 . P = 1/2.6 + 1/6.10 + 1/10.14 + ... + 1/198.202

4.1/2. P= 4/2.6 + 4/6.10 + 4/10.14 + ... + 4/198.202

2P=1/2-1/6+1/6-1/10+1/10-1/14+...+1/198-1/202

2P=1/2-1/202=50/101

P=50/101:2=50/101.1/2=25/101