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Gọi A=1/99x97-1/97x95-1/95x93-...-1/5x3-1/3x1

Suy ra A=-1/1x3-1/3x5-...-1/93x95-1/95x97-1/97x99

2A=-2/1x3-2/3x5-...-1/93x95-1/95x97-1/97x99

2A=-(2/1x3+2/3x5+...+1/93x95+2/95x97+1/97x99

2A=-(1/2-1/3+1/2-1/5+...+1/93-1/95+1/95-1/97+1/97-1/99)

2A=-(1/2-1/99)

2A=-97/198

A=-97/396

Đặt \(A=\frac{1}{99.97}-\frac{1}{97.95}-\frac{1}{95.93}-....-\frac{1}{5.3}-\frac{1}{3.1}\)

\(\Rightarrow A=\frac{1}{99.97}-\left(\frac{1}{1.3}+\frac{1}{3.5}+....+\frac{1}{93.95}+\frac{1}{95.97}\right)\)

\(\Rightarrow A=\frac{1}{99.97}-\frac{1}{2}\left(\frac{1}{1}-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+....+\frac{1}{95}-\frac{1}{97}\right)\)

\(\Rightarrow A=\frac{1}{99}-\frac{1}{97}-\frac{1}{2}\left(1-\frac{1}{97}\right)=\frac{1}{99}-\frac{1}{97}-\frac{1}{2}-\frac{1}{194}\)

\(\frac{-92}{93}\)

EM MỚI HỌK LỚP 6 THUI ẠK CHẮC K ĐÚNG HOẶC CÓ THỂ ĐÚNG ẠK NẾU ĐÚNG THÌ K ANH NHÓE!

CHÚC ANH HỌC TỐT

b: \(=9x^2+3x+1\)

0,2083.................

Đặt A=1/3x1 + 1/3x5 + ......+ 1/95x97 + 1/97x99

\(2A=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{97}-\frac{1}{99}\)

\(2A=1-\frac{1}{99}\)

\(A=\frac{98}{99}:2\)

\(A=\frac{49}{99}\)