Các bạn giúp mình giải bài 5), bài 6) và bài 7)
Bài 5.
Ta có:\(\dfrac{2022\times2021-1}{2021+2022\times2020}=\dfrac{2022\times2020+2022-1}{2021+2022\times2020}\)
\(=\dfrac{2022\times2020+2021}{2021+2022\times2020}=1\)
6)Ta có:\(\dfrac{18\times123+9\times4567\times2+3\times5310\times6}{\left(2+4+6+8+...+20+22\right)+48}\)
\(=\dfrac{18\times\left(123+4567+5310\right)}{\left(2+22\right)+\left(4+20\right)+..+\left(10+14\right)+12+48}\)
\(=\dfrac{18\times10000}{5\times24+60}=\dfrac{18\times10000}{5\times\left(24+12\right)}=\dfrac{18\times10000}{5\times36}=1000\)
7)Ta có:\(A=\dfrac{2021\times2021\times20202020-2020\times2020\times20212021}{2020\times20192019}\)
\(=\dfrac{2021\times2021\times2020\times10001-2020\times2020\times2021\times10001}{2020\times2019\times10001}\)
\(=\dfrac{2021\times2021\times2020-2020\times2020\times2021}{2020\times2019}\)
\(=\dfrac{2021\times2020\times2020+2021\times2020-2020\times2020\times2021}{2020\times2019}\)
\(=\dfrac{2021\times2020}{2020\times2019}=\dfrac{2021}{2019}\)
