Question

Giúp mình với

Answer 1

11) Ta có: \(\dfrac{1}{1\cdot2}+\dfrac{1}{2\cdot3}+\dfrac{1}{3\cdot4}+...+\dfrac{1}{12\cdot13}\)

\(=1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{12}-\dfrac{1}{13}\)

\(=1-\dfrac{1}{13}=\dfrac{12}{13}\)

Answer 2

Giải:

1/1.2+1/2.3+1/3.4+...+1/12.13

=1/1-1/2+1/2-1/3+1/3-1/4+...+1/12-1/13

=1/1-1/13

=12/13

Chúc bạn học tốt!