Question

Tính nhanh:

\(\dfrac{1}{2.50}+\dfrac{1}{5.8}+\dfrac{1}{8.11}+...+\dfrac{1}{90.93}\)

Answer 1

Đề sai nhá

Answer 2

\(\dfrac{1}{2.5}+\dfrac{1}{5.8}+...+\dfrac{1}{90.93}\)

\(=\dfrac{1}{3}\left(\dfrac{3}{2.5}+\dfrac{3}{5.8}+...+\dfrac{3}{90.93}\right)\)

\(=\dfrac{1}{3}\left(\dfrac{1}{2}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{8}+...+\dfrac{1}{90}-\dfrac{1}{93}\right)\)

\(=\dfrac{1}{3}\left(\dfrac{1}{2}-\dfrac{1}{93}\right)\)

\(=\dfrac{91}{558}\)

Answer 3

Đề sai hèn j giải mãi ko được. Không thấy được quy luật.