Question

Tính

\(\left(\frac{1}{4}-\frac{1}{5}-\frac{1}{20}\right)\left(\frac{2017}{2018}-\frac{2018}{2019}\right)\)

Answer 1

\(\left(\frac{1}{4}-\frac{1}{5}-\frac{1}{20}\right)\left(\frac{2017}{2018}-\frac{2018}{2019}\right)\)

= \(\left(\frac{1}{20}-\frac{1}{20}\right)\left(\frac{2017}{2018}-\frac{2018}{2019}\right)\)

= \(0\cdot\left(\frac{2017}{2018}-\frac{2018}{2019}\right)=0\)

Answer 2

Đặt \(\frac{2017}{2018}-\frac{2018}{2019}=A\)

Ta có : 
\(\left(\frac{1}{4}-\frac{1}{5}-\frac{1}{20}\right)\left(\frac{2017}{2018}-\frac{2018}{2019}\right)\)

\(=\left(\frac{5}{20}-\frac{4}{20}-\frac{1}{20}\right).A\)

\(=\left(\frac{1}{20}-\frac{1}{20}\right).A\)

\(=0.A\)

\(=0\)

Vậy ...

Chúc bạn học tốt !!! 

Answer 3

\(\left(\frac{1}{4}-\frac{1}{5}-\frac{1}{20}\right)\left(\frac{2017}{2018}-\frac{2018}{2019}\right)\)

\(=\left(\frac{5}{20}-\frac{4}{20}-\frac{1}{20}\right)\left(\frac{2017}{2018}-\frac{2018}{2019}\right)\)

\(=0\left(\frac{2017}{2018}-\frac{2018}{2019}\right)\)

\(=0\)