a) \(2021^{2020}-2021^{2019}=2021^{2019}.\left(2021-1\right)=2021^{2019}.2020\)
b) Ta có :\(7x-140=3.7^2\)
\(\implies\) \(7x-140=3.49\)
\(\implies\) \(7x-140=147\)
\(\implies\) \(7x=287\)
\(\implies\) \(x=41\)
c)175 - [(67 + 197)+ 33] : (11*32)
\(=175-\left(\left(67+33\right)+197\right):33^2\)
\(=175-\left(100+197\right):1089\)
\(=175-297:1089\)
\(=175-\frac{3}{11}\)
\(=\frac{1922}{11}\)
