(а/а+1+1):(1-3а^2/1-а^2)

To simplify the expression (а/а+1+1):(1-3а^2/1-а^2), we need to perform the following steps:

Step 1: Simplify the numerator of the expression. (a/а+1+1) = (a/(a+1) + 1) = (a + (a+1))/(a+1) = (2a+1)/(a+1)

Step 2: Simplify the denominator of the expression. (1 - 3a^2)/(1 - а^2) = ((1-а)(1+а))/((1-а)(1+а)) = (1+а)/(1+а) = 1

Step 3: Simplify the expression by dividing the numerator by the denominator. ((2a+1)/(a+1))/1 = (2a+1)/(a+1)

Therefore, the simplified expression is (2a+1)/(a+1).