Question

Tinh gia tri bieu thuc: A=2/2.5+2/5.8+............+2/95.98

Answer 1

\(A=\frac{2}{2.5}+\frac{2}{5.8}+...+\frac{2}{95.98}\)

\(A=\frac{2}{3}.\left(\frac{3}{2.5}+\frac{3}{5.8}+...+\frac{3}{95.98}\right)\)

\(A=\frac{2}{3}.\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+...+\frac{1}{95}-\frac{1}{98}\right)\)

\(A=\frac{2}{3}.\left(\frac{1}{2}-\frac{1}{98}\right)\)

\(A=\frac{2}{3}.\frac{24}{49}\)

\(A=\frac{16}{49}\)

_Chúc bạn học tốt_

Answer 2

A=2/2.5 + 2/5.8 +...+2/95.98

A=2 x(1/2.5 + 1/5.8 +...+1/95.98)

3A=2 x (3/2.5 + 3/5.8 +...+3/95.98)

3A=2 x  (1/2 - 1/5 +1/5 -1/8 +...+1/95 - 1/98)

3A=2 x (1/2 - 1/98)

3A=2 x 24/49

3A=48/49

=> A= 48/49 : 3

     A=16/49

Vậy A=16/49