Hello,
Why "Multiply the polynomial by distribution" ?
It's s t u p i d, you compliquate the equation.
In order to find the roots of P(a)=(a-3)(a²+2a-6)=0
a²+2a-6
=(a²+2a+1)-7
=(a+1)²-7
=(a-√7)(a+√7)
P(a)=(a-3)(a-√7)(a+√7)
Roots are 3,√7 and -√7
(If i have well understood the question , sorry if not)