a) Ta có:
`M - N = (2019.201.101.301)/(-2018.701.501) + (-301.101.201.2019)/(501.701.2018)`
`M- N = (-2019.201.101.301)/(2018.701.501) + (-301.101.201.2019)/(501.701.2018)`
`M-N= (-2019.201.101.301+301.101.201.2019)/(2018.701.501)`
`M-N = 0/(2018.701.501)`
`M-N =0`
`=> M =N`
Vậy `M=N`
b) `A= 1 + 1/3^2 + 1/3^4 +...+1/3^50`
`9A = 9(1+ 1/3^2 + 1/3^4 +...+ 1/3^50)`
`9A= 9 + 1/3 + 1/3^2 +...+1/3^48`
`9A-A = 9+ 1/3 +1/3^2 +...+ 1/3^48 - 1 - 1/3^2 -1/3^4-..-1/3^50`
`8A = 9- 1/3^50`
`=> n= 50`
Vậy `n=50`