Упростите выражение!

(a-1/a+1-a/a-1) * a+1/1-3a

(a / (a-1) + 1) : (1-3a^2 / (1-a^2) = = ((a+a+1) / (a+1)) : ((1-a^2-3a^2) / (1-a^2) = = ((2a+1) / (a+1)) : ((1-4a^2) / (1-a^2)) = = ((2a+1) / (a+1)) : ((4a^2-1) / (a^2-1)) = = ((2a+1) (a^2-1)) / ((a+1) (4a^2-1)) = = ((2a+1) (a-a) (a+1)) / ((a+1) (2a-1) (2a+1)) = = (a-1) / (2a-1)