Đáp án:
`a)`
` (x-7)/2020 + (x-7)/2021 = (x-7)/2020`
` => (x-7)/2020 + (x-7)/2021 - (x-7)/2020=0`
` => (x-7)(1/2020 + 1/2021 - 1/2020) = 0`
` => (x-7). 1/2021 = 0`
` => x - 7 = 0`
` => x= 7`
Vậy ` x = 7`
` b)`
` 1/(2)x - 1/(5)x +1 = 0`
` => x (1/2 - 1/5) +1 = 0`
` => 3/(10)x + 1 = 0`
` => 3/(10)x = -1`
` => x= -1 : 3/(10)`
` => x = -10/3`