Question

1/1x2 + 1/2x3 + 1/3x4 + ... + 1/99x100

tinh nhanh

 

 

Answer 1

1/1.2 + 1/2.3 + 1/3.4 + ... + 1/99.100

= 1 - 1 /2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/99 - 1/100

= 1 - 1/100

= 99/100

Answer 2

\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{99.100}=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{99}-\frac{1}{100}=1-\frac{1}{100}=\frac{99}{100}\)