Question

Tính nhanh: D= 1/99 - 1/99.98 - 1/98.97 - 1/97.96 -.....- 1/2.1

Answer 1

không đâu dễ mà

\(D=\frac{1}{99}-\frac{1}{99.98}-\frac{1}{98.97}-...-\frac{1}{2.1}=\frac{1}{99}-\left(\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{98.99}\right)=\frac{1}{99}-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{98}-\frac{1}{99}\right)=\frac{1}{99}-\left(1-\frac{1}{99}\right)\)

=\(\frac{1}{99}-\frac{98}{99}=-\frac{97}{99}\)

Answer 2

đề có thiếu ko