Question

Bài 1 : 

a) \(\frac{1}{1.2}\)+ \(\frac{1}{2.3}\)+.....+ \(\frac{1}{a\left(a+1\right)}\)

b) \(\frac{1}{1.2.3}+\frac{1}{2.3.4}+.....+\frac{1}{a\left(a+1\right).\left(a+2\right)}\)

 

Answer 1

a, \(\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{a.\left(a+1\right)}\)

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{a}-\frac{1}{a+1}\)

\(=1-\frac{1}{a+1}\)

b, \(\frac{1}{1.2.3}+\frac{1}{2.3.4}+...+\frac{1}{a.\left(a+1\right).\left(a+2\right)}\)

=\(\frac{1}{1.2}-\frac{1}{2.3}+\frac{1}{2.3}-\frac{1}{3.4}+...+\frac{1}{a.\left(a+1\right)}-\frac{1}{\left(a+1\right).\left(a+2\right)}\)

\(=\frac{1}{1.2}-\frac{1}{\left(a+1\right).\left(a+2\right)}\)

\(=\frac{1}{2}-\frac{1}{\left(a+1\right).\left(a+2\right)}\)

Chúc bạn học giỏi nha!!!

K cho mik vs nhé Hang Nguyen

Answer 2

Ý bạn là j z, tìm quy tắc để tính hả???!!!

Answer 3

Tính bạn ơi