Changes made to your input should not affect the solution:
 (1): "a2"   was replaced by  "a^2".  2 more similar replacement(s).
(2): Dot was discarded near "a.(".
Step by step solution :
Step 1  : (0+(3•(a2)))-a•(a-1)•(a+1))•(a+3))•(a2+1))•(a-3))•(a2-3))•(a+1))
Step  2  : (0+(3•(a2)))-a•(a-1)•(a+1)•(a+3))•(a2+1))•(a-3))•(a2-3))•(a+1))
Step  3  : (0+(3•(a2)))-a•(a-1)•(a+1)•(a+3)•(a2+1))•(a-3))•(a2-3))•(a+1))
Step  4  :Polynomial Roots Calculator :
Find roots (zeroes) of : Â Â Â Â Â Â F(a) = a2+1
Polynomial Roots Calculator is a set of methods aimed at finding values of  a  for which   F(a)=0 Â
Rational Roots Test is one of the above mentioned tools. It would only find Rational Roots that is numbers  a  which can be expressed as the quotient of two integers
The Rational Root Theorem states that if a polynomial zeroes for a rational number  P/Q  then  P  is a factor of the Trailing Constant and  Q  is a factor of the Leading Coefficient
In this case, the Leading Coefficient is  1  and the Trailing Constant is  1.Â
 The factor(s) are:Â
of the Leading Coefficient :Â Â 1
 of the Trailing Constant :  1Â
 Let us test
  P  Q  P/Q  F(P/Q)   Divisor     -1     1     -1.00     2.00        1     1     1.00     2.00  Â
Polynomial Roots Calculator found no rational roots
step  4  : (0+(3•(a2)))-(((a•(a-1)•(a+1)•(a+3)•(a2+1)•(a-3))•(a2-3))•(a+1))
step  5  : (0+(3•(a2)))-((a•(a-1)•(a+1)•(a+3)•(a2+1)•(a-3)•(a2-3))•(a+1))
Step  6  :Trying to factor as a Difference of Squares :
Factoring:Â Â a2-3Â
(Theory : A difference of two perfect squares,  A2 - B2  can be factored into  (A+B) • (A-B) )
Proof :  (A+B) • (A-B) =
        A2 - AB + BA - B2 =
        A2 - AB + AB - B2 =Â
         A2 - B2
(Note :Â Â AB = BAÂ is the commutative property of multiplication.Â
Note :Â Â -Â ABÂ + ABÂ equals zero and is therefore eliminated from the expression.)
Check : 3 is not a square !!Â
Ruling :Â Binomial can not be factored as the difference of two perfect squares.
step  6  : (0+(3•(a2)))-(a•(a-1)•(a+1)•(a+3)•(a2+1)•(a-3)•(a2-3)•(a+1))
Step  7  :Evaluate an expression :
Multiply  (a+1) by  (a+1)Â
The rule says : To multiply exponential expressions which have the same base, add up their exponents.
In our case, the common base is  (a+1) and the exponents are :
          1 , as  (a+1) is the same number as  (a+1)1Â
 and   1 , as  (a+1) is the same number as  (a+1)1Â
The product is therefore,  (a+1)(1+1) = (a+1)2Â
step 7  : (0+(3•(a2)))-a•(a-1)•(a+1)2•(a+3)•(a2+1)•(a-3)•(a2-3)
Step 8 : (0+3a2)-a•(a-1)•(a+1)2•(a+3)•(a2+1)•(a-3)•(a2-3)
Step  9  : Evaluate :  (a+1)2  =  a2+2a+1Â
Step  10  :Pulling out like terms :
 Pull out like factors :
   -a10 - a9 + 12a8 + 12a7 - 26a6 - 26a5 - 12a4 - 12a3 + 30a2 + 27a  =Â
  -a • (a9 + a8 - 12a7 - 12a6 + 26a5 + 26a4 + 12a3 + 12a2 - 30a - 27)Â
Final result : -a • (a9 + a8 - 12a7 - 12a6 + 26a5 + 26a4 + 12a3 + 12a2 - 30a - 27)
hoped this helped