Question

tinh gia tri bieu thuc lop 6 : 6/5.7+6/7.9+6/9.11+......+6/33.35

Answer 1

đặt A=6/5.7+6/7.9+6/9.11+......+6/33.35

\(\Leftrightarrow A=3\left(\frac{2}{5\cdot7}+\frac{6}{7\cdot9}+...+\frac{6}{33\cdot35}\right)\)

\(\Rightarrow A=3\left(\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{33}-\frac{1}{35}\right)\)

\(\Rightarrow A=3\left(\frac{1}{5}-\frac{1}{35}\right)\)

\(\Rightarrow A=3\cdot\frac{6}{35}\)

\(\Rightarrow A=\frac{18}{35}\)