Question

[nguyễn ngọc lam thanhh]

A= 1/1.2+1/2.3+1/3.4+...+1/49.50

A=2/1.3+2/3.5+2/5.7+....+2/49.51

A=1/2.4+1/4.6+1/6.8+....+1/18+20

Giúp e ạ,nhanh e tik ( ◜‿◝ )♡( ◜‿◝ )♡

Answer 1

[Lê Hồng Ngọc]

\(A=\) \(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{49.50}\)

\(A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{49}-\frac{1}{50}\)

\(A=1-\frac{1}{50}\)

\(A=\frac{49}{50}\)

Answer 2

[Lê Hồng Ngọc]

\(A=\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{49.50}\)

A= \(\frac{1}{1}-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{49}-\frac{1}{51}\)

A = \(\frac{1}{1}-\frac{1}{51}=\frac{50}{51}\)