Lm hộ mình 2 câu này và tìm ĐKXĐ luôn giúp

`color{#4B0082}{@ F}color{#560E8A}{r}color{#611C92}{e}color{#6C2A9A}{e}color{#7738A2}{d}color{#8246AA}{o}color{#8D54B2}{m} \ color{#9862BA}{S}color{#A370C2}{o}color{#AE7ECA}{l}color{#B98CD2}{v}color{#C49ADA}{e}color{#CFA8E2}{r}color{#DAB6EA}{s}`

a, ĐKXĐ: `a ne 1; a ne -1`

`A = a^2/(a+1) + 1/(a-1) - (2a)/(a^2-1)`

`A = (a^2(a-1))/((a+1)(a-1)) + (1(a+1))/((a-1)(a+1)) - (2a)/((a-1)(a+1))`

`A = (a^3 - a^2 + a + 1 - 2a)/((a-1)(a+1))`

`A = (a^3 - a^2 - a + 1)/((a-1)(a+1))`

`A = (a^2(a-1) - (a-1))/((a-1)(a+1))`

`A = ((a-1)(a^2-1))/(a^2-1)`

`A = a - 1`

b, ĐKXĐ: `x ne 0; x ne -6`

`A = 7/x - x/(x+6) + 36/(x^2+6x)`

`A = (7(x+6))/(x(x+6)) - (x*x)/(x(x+6)) + 36/(x(x+6))`

`A = (7x + 42 - x^2 + 36)/(x(x+6))`

`A = (-x^2 + 7x + 78)/(x(x+6))`

`A = -(x^2 - 7x - 78)/(x(x+6))`

`A = -(x^2 + 6x - 13x - 78)/(x(x+6))`

`A = -(x(x+6) - 13(x+6))/(x(x+6))`

`A = -((x+6)(x-13))/(x(x+6))`

`A = (13-x)/x`